CompactPCI Serial – Compendium

CompactPCI Serial – Compendium
CompactPCI Serial – Compendium
Both CompactPCI PlusIO and CompactPCI Serial is based on CompactPCI,
an established standard for building cost-effective, industrial and reliable
computers. Users appreciate the modularity, robustness and economic
efficiency of CompactPCI. With the new standards they get all these
advantages plus fast serial data transfer – including the migration path.
Content
CompactPCI Serial – Compendium ......................................................................................... 1
History of a New Standard ....................................................................................................... 4
CompactPCI Serial ................................................................................................................... 7
Architecture Overview ................................................................................................................................7
Key Characteristics ............................................................................................................................. 10
Wiring and Connectors ........................................................................................................................ 11
Look Back on CompactPCI: Keep What is Tried and Tested ............................................................. 13
Computer Set-Up as a Star and Mesh .................................................................................................... 13
Modern Computer Architecture ........................................................................................................... 13
Star Architecture with Ethernet, PCI Express, SATA and USB .......................................................... 15
The Special Role of Ethernet .............................................................................................................. 15
Identical Peripheral Slots .................................................................................................................... 17
Typical Tasks of the Serial Interfaces ..................................................................................................... 17
Ethernet for Complex Systems ........................................................................................................... 17
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The Ethernet Mesh .............................................................................................................................. 17
PCI Express for High Bandwidth ......................................................................................................... 24
SATA/SAS for RAID Systems ............................................................................................................. 27
USB for Mobile Functions ................................................................................................................... 29
Hot-Plug Functionality ............................................................................................................................. 30
Requirements for Hot Plugging ........................................................................................................... 30
Typical Applications............................................................................................................................. 31
Conduction Cooling ................................................................................................................................. 32
Convection Cooling ............................................................................................................................. 32
Conduction Cooling ............................................................................................................................. 32
Physical Addressing ................................................................................................................................ 34
Benefits and Pitfalls ............................................................................................................................. 34
Physical Addressing with CompactPCI Serial ..................................................................................... 34
Mechanics ............................................................................................................................................... 36
The Guide Element ............................................................................................................................. 36
Connector Usage and Coding ............................................................................................................. 37
Two Card Formats: 3U and 6U ........................................................................................................... 39
Extension using Mezzanine Cards ...................................................................................................... 43
Individual Rear I/O for 3U and 6U ....................................................................................................... 44
Application-Specific Backplane Architectures ..................................................................................... 46
Use in Harsh Environments: EN 50155 as an Example ......................................................................... 48
Spoiled for Choice: CompactPCI Serial or VPX? ................................................................................... 49
Migration using CompactPCI PlusIO .................................................................................... 51
Architecture Overview ............................................................................................................................. 51
Standardized Interfaces with CompactPCI PlusIO ............................................................................. 52
Hybrid Systems as a Bridge between the Standards .......................................................................... 53
PCI Express ............................................................................................................................................ 54
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Ethernet................................................................................................................................................... 55
Why BASE-T? ..................................................................................................................................... 55
Possibilities through Ethernet on the Backplane ................................................................................. 55
Electrical Specification ............................................................................................................................ 56
Interoperability ........................................................................................................................................ 57
Defined Interface Order ....................................................................................................................... 57
Implementation in Real Life ................................................................................................................. 58
Hybrid Systems ...................................................................................................................... 60
Using CompactPCI PlusIO...................................................................................................................... 60
The Important Role of CompactPCI PlusIO ........................................................................................ 60
Hybrid Possibilities using CompactPCI PlusIO ................................................................................... 61
Direct Connection between CompactPCI and CompactPCI Serial ........................................................ 63
Perspective ............................................................................................................................. 65
Abbreviations ......................................................................................................................... 67
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History of a New Standard
In 1994/95, Jim Medeiros of Ziatech and Joe Pavlat of Pro-Log, among others, presented a concept for
modular computers based on PCI bus plug-in cards in Eurocard format, connected to a passive
backplane. They called their concept CompactPCI. Soon, other companies such as Motorola, Radisys
(Intel) and Lucent showed interest in this concept and participated in its standardization. The CompactPCI
bus was successful and soon reached a high market penetration for industrial, reliable systems. It
became the most important standard in the telecommunications industry. But it also soon conquered
markets that had traditionally been occupied by the STD Bus or the VMEbus. Beside wide areas in
industrial environments, these were medical engineering, measurement and transportation. CompactPCI
was cleverly based on the IEEE 1101 mechanical standards for Eurocards and 19" systems known and
proven from the VMEbus. Finally, the conductive cooling solutions were also taken over so that even
military applications opened up for the CompactPCI bus.
During the last years the parallel PCI bus technology has more and more been complemented by fast
serial point-to-point connections. Depending on the types of peripherals and functions, different interface
standards are taking root. For example, SATA or SAS is the interface for mass storage devices like hard
disks. USB has established itself for Wi-Fi components and loosely coupled peripheral devices like
keyboards, touch screens, external hard disks etc. Beside the traditional network technology Ethernet is
also used as an interface for multiprocessing and as a fieldbus for decentralized I/O. PCI Express is used
for connection of closely coupled computer peripherals.
These interfaces coexist and each has its own special range of applications. A modern computer needs
all of them. Unlike in the past, however, they are not connected to separate controller chips which are
interconnected by a bus. In modern chip architectures all these interfaces are directly available at the
chipset. For this reason, the structure of a computer slowly changes from a bus-based system to a
system with a star topology connected by serial point-to-point connections.
The Next Generation of Modular Computers: First Attempts
Naturally, modular computers are still needed. As there are many different serial interfaces new
standards were created depending on the industrial range – optimized for the market and the application.
For example, AdvancedTCA has been created especially for telecommunication applications, whereas
standards such as VPX (ANSI/VITA 46.0) are focused on military applications.
Retroactively it was tried to make specialized standards universally usable again. One of these was
MicroTCA. For MicroTCA a computer system was defined based on the mezzanines standardized with
AdvancedTCA, the AMC. Due to the fact that originally this concept did not consider passive backplanes
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for the mezzanines, there were high infrastructure costs for emulating the AMC carrier board. What is
more, the mechanics are completely incompatible to IEEE 1101 (Eurocards and 19“ technology). The
amendments which were necessary later to make MicroTCA suitable for harsh environmental conditions
also present certain problems.
Another standard exclusively based on PCI Express – CompactPCI Express – was not able to penetrate
the market. This standard uses the IEEE 1101 but the limitation to PCI Express as the only interface type
is not sufficient.
The aforementioned system concepts all work with so-called switched fabrics, i.e. additional switches and
bridges which are required to connect each slot with the right interface. This causes higher costs for the
infrastructure, requires special software for the configuration and does not prevent that customer-specific
backplanes are needed. As there are a multitude of different options it is rarely possible to exchange
plug-in boards of different manufacturers 1:1.
For this reason, most modular computers are based on the CompactPCI standard which has proven itself
the world over. The serial point-to-point connections are realized as needed proprietarily via user-defined
pins. Unfortunately, this leads to a growing incompatibility of assemblies from different manufacturers.
Customized backplanes are needed to connect the serial buses. Is there a way that sustainably leads out
of this dilemma?
The Way into the Future: A Contemporary Concept
The aim is to develop a new concept that is future-proof but is based on the existing CompactPCI
standard and the proven and no doubt robust 19-inch technology:

It is supposed to allow for a smooth migration from the current standard to the modern point-to-point
connections.

It is also supposed to support all important serial interfaces on an equal footing, i.e. PCI Express,
SATA/SAS, USB and Ethernet.

The costs for the infrastructure have to remain low, which means that bridges and switches may only
be used as an exception.

It has to be possible to offer off-the-shelf backplanes, i.e. each slot has to be usable universally
without special routing.
PICMG (PCI Industrial Computer Manufacturers Group) has defined two standards for this – PICMG 2.30
CompactPCI PlusIO, ratified in November 2009, and PICMG CPCI-S.0 CompactPCI Serial, ratified in
March 2011.
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Backward compatibility across platforms
4xPCIe
PCI
32-bit
PCI
64-bit
„CompactPCI“
PICMG 2.0
(1999)
PCI
32-bit
PCI
64-bit
PCI
32-bit
up to
Gen2
6x4 PCIe
up to Gen3
PCI
2x8 PCIe
32-bit up to Gen3
„CompactPCI“
PICMG 2.0
PICMG 2.16
(2001)
„CompactPCI
PlusIO“
PICMG 2.30
(2010)
„CompactPCI
Serial“
CPCI-S.0
(2011)
2x Gb Eth.
Up to 4x Gb Eth.
Up to 10x Gb Eth.
parallel
hybrid
serial
Overview of CompactPCI and the new serial standards
A New Base Specification
The structure of PICMG's specifications always follows the same principle: A base specification is
extended by follow-on standards. The base specification of the well-known, widely used CompactPCI
standard is designated PICMG 2.0. The zero after the point indicates that this is a base specification.
Standards building on it and extending it have higher numbers with the same prefix. PICMG 2.16, for
instance, describes Ethernet over the backplane for 6U CompactPCI. PICMG 2.30 – CompactPCI PlusIO
– defines the usage of the user I/O signals of backplane connector J2 for 3U and 6U boards, in order to
make modern serial buses usable together with the parallel PCI bus. In this way, PICMG 2.30 details
PICMG 2.0 CompactPCI.
CPCI-S.0 is the base specification of the new CompactPCI Serial standard. On the one hand a base
specification defines as little as possible to stay open for later technological change, but on the other
hand this specification needs to be complete enough to guarantee smooth interoperability of the products
of different manufacturers – which in the end is, or at least should be, the basic idea of a standard.
Being a base specification, CPCI-S.0 must not refer to other base specifications. The mechanics of
parallel CompactPCI is basically identical with CompactPCI Serial. Still, CPCI-S.0 must again describe all
the technical details. On the one hand CompactPCI Serial is widely redundant to CompactPCI, but on the
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other hand a standard like this is easy to read, because this way one document contains all the
technically relevant details.
CompactPCI Serial
Architecture Overview
CompactPCI Serial is a design update for the proven CompactPCI. The new base standard of PICMG
named CPCI-S.0 completely replaces the parallel signals by fast serial data transfer and introduces a
new connector type. This way, CompactPCI Serial supports all modern point-to-point connections while
keeping mechanical compatibility with IEEE 1101 and with the Eurocard format.
CompactPCI Serial is based on a simple, complete star topology equally for PCI Express (optionally also
Serial Rapid IO, SRIO), SATA/SAS and USB. The system slot supports up to eight of these peripheral
lots. No bridges or switches are needed for a system with up to nine slots.
I/O
I/O
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Ser CI
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Per al
.
I/O
c
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Pe ria I
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CI
cP rial
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I/O
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Per.
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r.
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Star architecture with CompactPCI Serial
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In principle all peripheral slots are identical. Only two are connected to the system slot using an extra
wide PCI Express link called a Fat Pipe. These slots can be used for a high-end graphics extension, for
example.
System
Slot 0
Fat Pipe Fat Pipe
Perip.
Perip.
Slot 1
Slot 2
Perip.
Slot 3
Perip.
Slot 4
Perip.
Slot 5
Perip.
Slot 6
Perip.
Slot 7
Perip.
Slot 8
P6
P5
P4
P3
P2
P1
Slots in a CompactPCI Serial system
Ethernet is not wired as a star but as a full mesh network. In full mesh architectures each of the nine slots
is connected to each of the other eight slots via a dedicated point-to-point connection. The wiring pattern
has been chosen in such a way that – if a CPU board only supports two Ethernet interfaces – three slots
are completely wired – even without switches, routing etc.
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I/O
I/O
cP
Ser CI
i
Per al
.
I/O
c
Se PC
Pe ria I
r. l
CI
cP rial
Se er.
P
I/O
cPCI
Serial
Per.
I/O
cPCI
Serial
Per.
cPCI
Serial
SystemSlot
c
Se PCI
Pe rial
r.
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cPeria .
S Per
I/O
I
cPCial
Ser r.
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Full Mesh using Ethernet
Contrary to other concepts, the Ethernet transmission on the backplane is based on the proven standards
for copper connections – 100BASE-T, 1000BASE-T and 10GBASE-T. This offers the advantage of
unlimited interoperability even for different data rates. Electrical isolation is possible at least optionally,
which ensures the absence of feedback from the boards. This is important for redundant, safety-critical
systems. Besides, several systems can easily be connected to each other.
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Key Characteristics
Interface Type
System Slot
Peripheral Slot
PCI Express
6 x4 links
1 link, maximum x8
2 x8 links (fat pipes)
SATA/SAS
8 channels
1 channel
USB 2.0
8 channels
1 channel
USB 3.0
8 channels
1 channel
Ethernet 10GBASE-T
8 channels
Up to 8 channels
CompactPCI Serial: Interfaces for system slot and peripheral slot
In addition, there are a number of signals to support these interfaces and for general system
management, such as reset, IPMB, hot plug, geographical addressing, etc.
12 V are available for power supply, allowing a maximum power consumption of 60 W for one 3U slot.
This includes the peripheral slots. The interfaces are all accessible at the same time. This is important, for
example, for PCI Express Mini Cards, which expect USB as well as PCI Express support.
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Wiring and Connectors
Star Topology using an Ethernet Mesh
The architecture of CompactPCI Serial is a simple star of one system slot and up to eight peripheral slots,
combined with a full mesh for Ethernet. The pin assignment for Ethernet is the same for the system slot
and peripheral slots. One pin signals to the plugged-in board whether it is located in a system slot or
peripheral slot.
This allows to plug a system-slot board (normally a CPU card) also into any peripheral slot. In this case
some interfaces are not supported, of course – usually SATA. The Ethernet interfaces are always
supported, however. Despite its star topology CompactPCI Serial supports symmetrical multiprocessing
with up to nine CPUs in one system – without bridges and without a special backplane. With bridges even
more are supported.
The New Connector Type
The usage of a new connector type allows for the necessary high signal density and high transmission
frequencies of 12 Gbit/s and more. The AirMax connector (FCI, Amphenol TCS) offers space for up to
184 pin pairs on a 3U board. The high pin number is especially important for the system slot because of
the above-mentioned star architecture of modern computers. It also allows using a multitude of free pins
for customized rear I/O on peripheral assemblies. The mechanics of the connector meet the requirements
of the IEEE 1101 and the look-and-feel is very much like that of the proven 2-mm-connector of the
CompactPCI standard.
Compared to CompactPCI, the placement of the plug and receptacle connectors is swapped. The plug
connector is placed on the plug-in card, while the receptacle connector is located on the backplane – just
as in VMEbus systems. This makes twisted pins on the backplane a thing of the past.
CompactPCI Serial: Compared to CompactPCI the plug and receptacle are swapped
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The AirMax connector was specially developed for use in harsh environments. For the plug connector, i.e.
the connector on the plug-in card, there are versions that can be mounted side by side. They only have
two walls. In other varieties the pins are enclosed by three or four walls.
CompactPCI Serial: Different versions of the AirMax connector
On a 3U board, there is always one connector with four walls and six pin rows. It is supplemented by
several types mounted side by side and having two walls and eight rows. The final connector has three
walls and eight rows.
CompactPCI Serial: Row of connectors on a plug-in board
On the whole this makes a plug connector that is protected on all sides and has a crossing wall at the
center. This crossing wall supports the stability of the plug-in board, while preventing a CompactPCI
Serial board from being plugged into a conventional CompactPCI slot and from twisting the pins there.
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Look Back on CompactPCI: Keep What is Tried and Tested
CompactPCI Serial is a design update to the proven CompactPCI. Together, they provide a future-safe
platform for industrial computers. The architecture adapts to modern chipsets. As the mechanics are
100% compatible with IEEE 1101, you can use all standard 19“ system solutions without limitations. The
dimensions of the backplanes are identical to those of the CompactPCI backplanes and are fixed in the
same way. Front panels and handles have not been changed either. The well-proven hot plug mechanics
– the switch in the handle – remains the same and acquires a new meaning for hard disk RAIDs. Only the
connector is replaced by a modern type which is able to support the high frequencies.
Computer Set-Up as a Star and Mesh
Modern Computer Architecture
Today's computer architectures no longer use parallel buses but point-to-point connections. With the
parallel PCI bus disappearing, they now use a simple star topology. At the "center" there is the CPU
chipset that is surrounded by peripherals like the points of a star. It centrally addresses the peripheral
devices and components via PCI Express, USB, Ethernet or SATA – all of them serial point-to-point
connections.
The electrical characteristics of these serial connections are easier to manage and they permit higher
data transmission rates with fewer pins. With just one link (i.e. one differential receive and one transmit
line), PCI Express already achieves 250 MB/s. Other bus participants do not limit the bandwidth of this
connection. There is no direct influence. A higher number of links for a connection or a higher clock
frequency further increase the data rate (up to 16 GB/s with PCIe 3.0) – and all this with full-duplex
operation.
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USB
Printer
Graphics
PC
Ie
B
US
he
Et
rn e
SA
TA
Processor
Ext. Hard
Drive
t
Int. Hard
Drive
Router
Traditional set-up of a computer system in star shape
This structure was used 100% for CompactPCI Serial. The system slot is the center of the star. Each
peripheral board is a symmetrical point. This is inexpensive and simple. Suitable connectors are available
– now also in rugged designs.
A Challenge: Modular and Inexpensive, Without Switched Fabrics
The star architecture is a technical challenge for the system slot and the backplane with modular
computers like CompactPCI. The system slot must now provide a large number of connections. The
backplane must spread all of these connections to the peripheral slots without needing too many layers.
Standards like MicroTCA have defined switched fabric slots for this reason. These route the data over
special backplanes as desired.
CompactPCI Serial intentionally does without such mechanisms, and without bridges and switches. A
high reusability of standard components is essential for a cost-effective, modular computer system – in
the end, the costs of a modular computer must stay competitive compared to non-modular computers.
This does not mean that you could not integrate any switched fabrics into a CompactPCI Serial system, if
you wanted to build up complex structures, but you simply don't have to. Simple systems do have a
market share of around 90% of all CompactPCI systems.
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Star Architecture with Ethernet, PCI Express, SATA and USB
The star is supposed to be flexible and universal. This is why it must be able to control as many
different devices as possible – but which? PCI Express as a replacement for PCI is especially used in
a computer to communicate with further controller chips. It is the computer's classic "bus" extension and
is software-compatible with its predecessor PCI.
But even serial connections need many connection lines. For PCI Express, there is at least one line pair
for clock, one pair to receive data, and one pair to transmit data. To increase the bandwidth, you use
several lanes, so that one connection can easily count nine line pairs or more. Because of the high data
rate you also need to assure sufficient signal integrity, resulting in additional ground lines – at least one
per signal pair.
Mass storage devices today are controlled using SATA, especially hard disks that are directly built into a
computer. A RAID system where the hard disks are included as individual plug-in cards is a typical
example of this. USB is another feature that you can hardly imagine not to find in a state-of-the-art
computer.
There are three main fields of application for USB: removable storage (USB Flash drives, hard disks for
data back-up etc.), wireless interfaces (GSM, UMTS, GPS, Wi-Fi) and the replacement of the classic
serial interface. FTDI has set standards here. Devices that were formerly controlled directly via an
RS232/RS485 interface are now serviced through a USB-to-serial converter. USB 2.0 is an established
standard. USB 3.0 will be integrated in the latest chipsets of Intel, AMD and so on. Computers are
interconnected using Ethernet, so that Ethernet needs to be another point of the star.
The Special Role of Ethernet
For Ethernet, CompactPCI Serial supports a full mesh network. This backplane wiring creates a
dedicated connection of every slot with any other slot. Each of the nine slots in a CompactPCI Serial
system is connected with each of the other eight slots via the backplane. (You can find more on the
Ethernet mesh in Chapter The Ethernet Mesh.)
Ethernet has taken hold as the interface for multicomputer systems. Since CompactPCI Serial allows
using a system-slot CPU also as a peripheral card without any problems, it could hardly be simpler to
build up modular systems. All CPU boards communicate via Ethernet. As these are point-to-point
connections, no switch board is needed. Also, no special infrastructure or configuration is required.
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Copper-Based Standards
CompactPCI Serial supports copper-based standards for Ethernet (10/100/1000BASE-T and 10GBASET). These standards offer important advantages compared to special Ethernet backplane standards:

interoperability through autonegotiation even for different data rates

support of standard Ethernet chips

partly Ethernet controllers already included in the chipset

extremely robust and fault tolerant

no retroaction of the boards in case of a failure due to inductive or capacitive coupling

easy expandability with more than nine plug-in boards even between board enclosures

optional extension by standard Ethernet switches
One drawback is the higher number of lines: four line pairs per connection compared to two in the
Ethernet backplane standard 1000BASE-BX. This standard only supports 1 Gbit/s, though. As many as
eight line pairs are needed for 10GBASE-BX4 – with autonegotiation posing problems here. BASE-T is
the future technology here, as it is simpler.
Simple but Flexible Set-Up
Does this mean that each CompactPCI Serial board has to be equipped with eight Ethernet channels?
Not at all! Ethernet on the backplane is an option. Even with only one channel, communication with a
second, identical card is possible. If there are two channels, a full mesh network with three CPU cards is
possible, with three channels four boards can be interconnected etc. The backplane wiring was chosen in
such a way that even with fewer interfaces all CPU boards are still completely wired if they are plugged
next to each other.
CompactPCI Serial enables easy and cost-efficient multiprocessing based on Ethernet communication.
Let us sum up the fundamental benefits:

no switch boards are required in systems with up to nine slots

full mesh network even with fewer Ethernet channels

interoperability and future-safety by using BASE-T standards
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Identical Peripheral Slots
For a modular computer to be simple and transparent in use, every peripheral slot must have the same
features, i.e. must support all interfaces. Then the user does not need to be concerned about which slot
supports which board.
With CompactPCI Serial all eight peripheral slots are identical, each supporting 1 PCIe x4, 1 SATA, 1
USB 2.0, 1 USB 3.0 and 1 Ethernet directed to the system slot. Every board can be plugged into every
slot. There is only one exception: two slots support an additional PCIe x8 each. There are three main
high-bandwidth applications for this addition: graphics, high-end telecommunications and CompactPCI
Serial systems with more than eight peripheral slots. (You can find more on this in Chapter PCI Express
for High Bandwidth.)
Typical Tasks of the Serial Interfaces
Ethernet for Complex Systems
CompactPCI Serial supports both star architecture and a full mesh network for Ethernet. While star
architecture is fully sufficient for standard computers, a full mesh architecture is better suited for complex
multicomputer systems.
The Ethernet Mesh
In a full mesh, one Ethernet interface of every board is connected to exactly one Ethernet interface of
another board. With a standard, nine-slot backplane you need eight Ethernet channels on every board, so
that every board can communicate independently with any other board. As mentioned before, you do not
have to fully use this option.
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CPU
Eth
Eth
Eth
Eth
LAN
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
CPU
CPU
Eth
Eth
Eth
CPU
Full mesh with four boards, each based on three Ethernet channels
The above example shows how you can implement symmetrical multiprocessing in a CompactPCI Serial
system. This way, you can also realize an architecture of intelligent subsystems:
CPU
Subsystem
Eth
Switch
LAN
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
CPU
CPU
Eth
Eth
Eth
CPU
Ethernet mesh for an intelligent subsystem
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You can also connect the mesh network in the shape of a ring. This allows you to create redundant
structures in an elegant and inexpensive way, where the failure of one plug-in board does not cause the
failure of the entire system:
CPU
Eth
Switch
LAN
Switch
Switch
Eth
Eth
Eth
CPU
Switch
CPU
Eth
CPU
Ethernet mesh in ring structure
These are only some examples of architectures which can be realized using CompactPCI Serial. And all
this can be done with standard backplanes and standard boards. All of the four boards shown in the
above examples can be of the same type. Ethernet usage is determined by software.
As CompactPCI Serial is physically based on the BASE-T standards (10/100/1000BASE-T and
10GBASE-T), you can equip the boards with "common" Ethernet controllers. You can normally do without
electrical or optical isolation between the boards. This allows capacitive coupling, saving space and costs.
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Ethernet Mesh for Computer Clusters
If some years ago supercomputers were still built up of systems with a special technology, today mostly
standard computer technologies are used. For this, a large number of single comparatively cost-effective
servers are combined to form computer clusters.
A computer cluster in most cases consists of a large number of single interconnected computers which
are used to process parts of a total task in parallel. Seen from the outside a computer cluster acts as a
single computer. The nodes are interconnected using a fast network. Building such server farms
considerably increases the computing capacity and availability. In particular, the failure safety of a cluster
compared to that of a single computer is a decisive advantage. If a system within a cluster fails, this has
no direct influence on all other systems which are part of the cluster. This way redundancy is achieved.
Mainly two kinds of computer clusters are distinguished:

High-availability clusters are supposed to increase availability and ensure better failure safety. In
case of an error, the tasks of the defective host of the cluster are automatically transferred to another
host. Areas of usage are applications in which down-times of only some minutes per year maximum
are allowed.

High-performance computing clusters are used to carry out calculations that are distributed over
several hosts. From the user's point of view the cluster is a central unit, but which, from a logic point
of view, consists of several networked systems. Fields of application are mostly found in the areas of
science and military, but server farms for rendering 3D computer graphics and computer animations
are also built up of this kind of cluster.
The CompactPCI Serial architecture is predestined for building high-availability clusters. But also for
compact systems with high computing performance, solutions based on CPCI-S.0 are hard to beat.
The distribution computer responsible for this part of the cluster is plugged into the system slot, for
example. It is connected to the eight cluster nodes via a 1 Gbit/s (optionally 10 Gbit/s) full-mesh Ethernet
network. Such a 9-slot unit is a typical sub-cluster in a cluster network. Based on modern Intel technology
it provides 9 x 4 = 36 cores with 4 GB memory each, for instance. For availability reasons, the subcluster, which has a typical power consumption of 400 W, is equipped with its own PSU, which can also
be redundant if required.
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Computer cluster with CompactPCI Serial
Eight of the sub-clusters are connected via Ethernet to form one cluster. A CompactPCI Serial computer
is used for central management tasks as an NAS (Network Attached Storage). In total, the system has
288 cores plus management units. This cluster computer consisting of CompactPCI Serial components
has a power consumption of only 3500 W and needs 20 U in a 19" cabinet. The total volume of the
CompactPCI Serial cluster is only 50% of that of a solution with 1U servers. If required, it is also suited for
operation in extreme temperature ranges and in mobile applications.
Ethernet in Safety-Relevant Systems
Safety-relevant computers often use the principle of redundancy to detect errors. If two computers are
combined, this is called a 2-out-of-2 system. These two computers are often diverse, i.e. they differ, to
avoid the occurrence of what are called common cause errors. Besides safety, availability is also of
special importance for applications in critical areas.
Availability is also achieved through redundancy. If non-diversitary subsystems are extended by another
subsystem, you get a 2-out-of-3 system. For diversitary 2-out-of-2 systems, the desired availability is
achieved by doubling the whole 2-out-of-2 system.
The computers have to compare and align their results. To do this, they need an interface which on the
one hand offers a high enough data transfer rate and on the other hand guarantees absence of feedback.
After all, the defect of one computer is not supposed to paralyze the whole system. Ethernet, especially
the electrically isolated communication standards (10/100/1000BASE-T and 10GBASE-T) are particularly
well-suited.
CompactPCI Serial – Compendium
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CompactPCI Serial particularly focuses on safety-relevant systems. For this reason, additional features
such as hot plugging are included beside Ethernet as the communication interface. A board can be
removed from the system without interrupting the function of the other computers. As the communication
between the boards is based on Ethernet which implicitly supports hot plugging already, not even a
special hot plug controller is needed for this function. A single 12V power rail is used as the main power
supply. Building up redundant PSUs is especially simple if they only have to supply one output voltage.
A 2-out-of-3 system might for example consist of three CompactPCI Serial subsystems. Each subsystem
would have its own independent standard backplane with possibly independent PSUs. The connection of
the subsystems can be done via Ethernet and rear I/O (another advantage of BASE-T).
For wiring 2-out-of-3 systems, a full-mesh-architecture is well suited. A standard backplane
accommodates three identical CPU boards. Switches, which are also redundant, can also be realized as
independent CompactPCI Serial components on standard backplanes. The wiring of the subsystems
among each other is possible with rear I/O. A customer-specific backplane will be helpful for optimizing
this system function.
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
Eth
CPU
CPU
CPU
Switch
Switch
LAN
LAN
CPU
CPU
2-out-of-3 system with Ethernet full mesh architecture
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Modular Set-Up using Mezzanines
Ethernet mezzanine boards are plugged directly onto the system slot CPU and lead up to eight Ethernet
ports to the backplane via the dedicated P6 connector. They are used for the communication with
(intelligent) peripheral slot boards in a star or mesh architecture.
A special feature of these Ethernet mezzanines is that the CompactPCI Serial system connector P6,
where the Ethernet signals are routed to, is not located on the CPU board but directly on the mezzanine.
In contrast to previously known mezzanine standards, the signals are led directly to the backplane and do
not have to be routed over the carrier board.
P6
P5
P4
P3
P2
P1
Mezzanine with backplane connector P6 for Ethernet configuration of the system slot CPU
Another advantage of mezzanines is the flexible number of channels. The requirements can vary greatly,
depending on the application. Nevertheless, you can always use a standard CPU card.
For building up a full mesh network for all nine plug-in boards, you would need one mezzanine each with
the maximum of eight channels, in order to independently communicate with any other board. In simpler
multiprocessing systems where a star architecture is sufficient, the same mezzanine module is used – in
this case only once plugged onto the system slot CPU.
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Ethernet at the Front using Peripheral Boards
A possibility for using Ethernet at the front are CompactPCI Serial peripheral boards. These cannot only
be operated in pure CompactPCI Serial systems, but also ensure fast connection in hybrid systems with a
system slot according to CompactPCI PlusIO. (You can find more on hybrid systems in Chapter Hybrid
Systems.)
Using specialized peripheral cards has many benefits for particular requirements:

high data rates

special configuration options, e.g., simultaneous operation of all channels, or optionally two redundant
channel pairs

usage of fiber-optics connections (e.g., 1000BASE-SX)

design for harsh environments, e.g., for an operating temperature of -40 to +85°C

configuration for market requirements, e.g., with M12 instead of RJ45 connectors for railway
applications
Ethernet interface cards are peripheral boards that extend the number of the available ports of the system
slot CPU on a separate slot. The connection is done via PCI Express on the P1 connector. Switch boards
offer additional possibilities. Using an Ethernet switch in the system slot, multicomputers with CPU boards
in the peripheral slots can be built up, for instance – via the P6 connector. A switch in the peripheral slot
on the other hand offers the typical characteristics needed for connecting external devices – without
software overhead.
PCI Express for High Bandwidth
Contrary to other serial interconnects such as SATA and USB 3.0, PCI Express is not limited to a single
lane (a differential receive and transmit signal line pair) but combines up to eight of these lanes in parallel
(PCI Express x8).
This makes PCI Express perfect for high bandwidths. CompactPCI Serial systems, too, use it wherever a
lot of data are transmitted, especially for backplane communication between the CPU board and highperformance peripheral boards. Based on PCI Express 3.0, theoretical data rates of 8 GT/s per lane and
direction between boards and a total of more than 80 GB/s (bidirectional) inside the system are possible.
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Graphics
Similar to a classic PC, a modular computer is supposed to be able to control displays, too. Many
chipsets have a built-in graphics controller today. As a rule, the CPU and graphics controller share the
main memory in this architecture. This way, cost-effective and well-fitting solutions can be achieved for
low to medium requirements especially in the 2D area.
If displays with a very high resolution are to be controlled, the bandwidth of this shared memory reduces
both the performance of the CPU and of the graphics unit. If you want to operate several high-resolution
displays at the same time or if you have higher requirements regarding the graphics itself (e.g., 3D
rendering), it is advisable to use an external, independent graphics controller with its own video memory.
If you choose an external graphics controller, the data transfer rate of the connection between the chipset
and the graphics controller is the critical factor for the performance. For this reason, this connection has
significantly promoted the development of PCI Express.
Especially for controlling the graphics card, you often use the complete bandwidth, i.e. PCI Express x16.
As it is relatively frequent that more than one graphics card has to be controlled, all common chipsets and
graphics controllers support a mode which splits the PCI Express x16 link into two x8 links. This splitting
halves the maximum burst data rate. This is compensated for, however, by the constant advancement of
the transmission frequency at the PCI Express interface (PCIe 1.0, PCIe 2.0, PCIe 3.0 etc).
Special Architecture for Graphics Extensions
Graphics extensions are one reason for the special CompactPCI Serial architecture. Two slots are
connected to the system slot via two PCIe x8 interfaces. This way, two peripheral slots of a CompactPCI
Serial system that uses a standard backplane can be equipped with high-performance graphics cards.
As all other peripheral slots are driven using PCIe x4, you can generally plug graphics cards into any
peripheral slot. The performance is not quite as high there, but still sufficient for many applications.
Modern graphics chips are able to control up to four high-resolution displays simultaneously via
DisplayPort. A CompactPCI Serial system can accommodate up to eight graphics cards without using
bridges, making it possible to control 32 displays with the corresponding software.
CompactPCI Serial – Compendium
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19" system with eight graphics cards for control of 32 displays
This extensibility shows that the CompactPCI Serial architecture is very well suited for applications which
far extend the possibilities of the parallel CompactPCI. You can now even equip control rooms of power
stations, railway control centers, or even video walls with CompactPCI Serial systems.
Networking
The second classic application for PCI Express is in networking. Ethernet controllers and switches in
high-end telecommunications also need high bandwidth. In many cases, it is DSP or FPGA based boards
that benefit from PCIe x8. For these applications, it makes sense to use 6U boards, which also benefit
from the rear I/O functionality of CompactPCI Serial. 6U boards can communicate with their I/O via any
type of connector – even optical – in the rear area of the system. You can find more on this in Chapter
Individual Rear I/O for 3U and 6U.
Extending Peripheral Slots using Switched Fabrics
Another application is CompactPCI Serial systems with more than eight peripheral slots. For high-end
systems, you can plug a switched fabric board into the system slot instead of a classic CPU. The CPU is
located in a peripheral slot and communicates with the switched fabric via PCIe x8. The latter forms the
interface to several CompactPCI Serial subsystems, in order to implement complex systems with 9+8 or
with 9+16 slots.
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SATA/SAS for RAID Systems
An important reason for extending CompactPCI to CompactPCI Serial was the possibility to realize RAID
systems. For this reason SATA/SAS signals are available on the backplane beside the other interfaces.
This way, you can use every peripheral slot as a hard disk slot. The system slot can then control up to
eight hard disks – again in a star layout.
In a hybrid system, where the backplane brings together CompactPCI Serial peripheral boards with a
conventional CompactPCI CPU or a CompactPCI PlusIO CPU in the system slot, you can at least control
up to four hard disks. You can find more on CompactPCI PlusIO and hybrid systems in Chapter Hybrid
Systems.
The CompactPCI mechanics, which has been taken over unchanged for CompactPCI Serial, offers all
characteristics that a RAID shuttle needs:

Robust plug-in mechanics

switch in the handle to signal removal of the hard drive

(blue) LED to signal that the board may be removed
RAID System as a Multiprocessor NAS
With a centralized Ethernet connection the system can also act as an NAS (Network Attached Storage). A
RAID system like that might look as follows:
Switch
LAN
Eth
Eth
Eth
Eth
Eth
CPU
CPU
CPU
CPU
Hard
Drive
Hard
Drive
Hard
Drive
Periph.
Slot
Periph.
Slot
Periph.
Slot
Periph.
Slot
Periph.
Slot
Periph.
Slot
SATA
RAID
System
Slot
RAID system with NAS connection
CompactPCI Serial – Compendium
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In this system with several CPUs, all CPU boards are identical, but only the CPU in the system slot uses
its RAID controller and also has a plug-on switch to communicate with the other three CPUs over the
backplane. These are plugged in the peripheral slots and have neither a switch nor a RAID function in the
system.
Usage of SGPIO
CompactPCI Serial includes even more mechanisms that are required for a RAID system. For example it
is possible to determine the disk to be changed through the physical addressing. A management bus
which is compliant to the SFF-8485 specification provides the necessary communication between the
RAID controller and the shuttle. SFF stands for Small Form Factor Committee, www.sffcommittee.org,
where companies like Seagate, Sun, LSI, IBM and Intel push new standards.
The SFF-8485 standard defines a serial GPIO bus (SGPIO) especially in connection with Serial Attached
SCSI (SAS) and Serial ATA (SATA). It serves for exchanging data between the RAID controller and the
hard disk shuttle. It can transmit simple status information (e.g., "switch closed", "hard-drive powered")
and control LEDs or monitor the power supply of the hard drive. The SGPIO bus is dedicated to the
SATA/SAS functionality and independent of the system management bus of the CompactPCI standard.
The SGPIO bus uses four signals for data transmission:

SClock: a clock cycle signal driven by the RAID controller

SLoad: a synchronization signal to determine the start and the end of a transmission frame – also
driven by the RAID controller

SDataOut: the data output signal of the RAID controller

SDataIn: the data input signal of the RAID controller. Here the shuttles transmit the status information
while the time slot in the data frame corresponds to the physical address.
Extensions over the Backplane
Using SATA port multipliers even more than eight drives can be controlled in a CompactPCI Serial
system. For this, a custom backplane is needed which can have more than eight SATA/SAS slots. A
customer-specific solution could be to only specify part of the slots for SATA/SAS. Such a system could
for example consist of eight slots for PCI Express, USB and Ethernet as well as of eight additional slots
for SATA/SAS hard drives.
You can find more on specific backplanes in Chapter
Application-Specific Backplane Architectures.
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USB for Mobile Functions
While PCI Express is a relatively common backplane interface, USB seems to be rather unusual. USB is
in fact a widely used standard for the connection of peripheral devices like keyboard and mouse, USB
Flash drives and external hard disks especially to mobile computers.
Nearly all modern laptops also provide what are called Express card slots. These allow to retrofit the
computer externally, for instance by GSM/UMTS modems. Express cards are based on USB and
alternatively on PCI Express. Internally, laptop computers also use both interfaces to connect so-called
PCI Express Mini Cards.
In order to be able to use all PCI Express Cards and PCI Express Mini Cards even in a modular 19"
computer, you must also support these electrical interfaces – both USB and PCI Express in one slot. This
way you can equip CompactPCI systems with wireless technology.
To keep things most simple for the users, they should be able to put any board into any slot. This is the
case with CompactPCI Serial. The CPU centrally controls USB and PCI Express, and distributes the
signals to each of the eight peripheral slots via the backplane.
Modules with a higher bandwidth usually use a PCI Express interface (e.g., WLAN), while USB is
sufficient for modules with a lower bandwidth such as GSM/UMTS. With just one link (i.e. one differential
receive and one transmit line), PCI Express v1.x already achieves a bandwidth of 250 MB/s. USB 2.0 falls
far behind with its 480 Mbit/s. However, USB 3.0 reaches bandwidths similar to PCI Express.
CompactPCI Serial defines both USB 2.0 and USB 3.0, making it future-proof.
CompactPCI Serial peripheral card for PCI Express Mini Cards with antenna connectors at the front for wireless
communication
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Hot-Plug Functionality
The possibility to change individual assemblies during operation without damaging them and without
disturbing the function of the computer is called hot plugging. This is a very useful feature particularly for
modular computers. At the same time it has originally caused great efforts. This is different with
CompactPCI Serial.
As the CPCI-S.0 specification consequently works with serial interconnects, many technical problems are
solved implicitly. Ethernet, USB, PCI Express and SATA already support hot plugging. Naturally, some
(simple) measures are required in order to be able to use this in a 19" system according to IEEE 1101.
Requirements for Hot Plugging
Power Supply
Minimum requirements concern the power supply, for example: In the instant of a load reversal due to
plugging in or out a board it has to be ensured that the voltage remains in the allowed range. However, as
the main voltage is 12 V, the tolerance is very high here. In addition, the module may not cause too high a
surge current – with modern voltage regulators, the so-called soft start is state-of-the-art, however.
Slots and Hot-Plug Controllers
If you remove a board, you want to know which slot is concerned. Physical addressing enables this using
four pins on the backplane. To access this information an interface to the hot-plug controller is needed.
When is a hot-plug controller required?
If a peripheral board is based on Ethernet, for example, no controller is needed at all. This only works,
however, because CompactPCI Serial is based on Ethernet standards for copper cables (100/1000BASET and 10GBASE-T). The situation is similar for assemblies based on USB – but here software
interactions are often required ("You can now remove the device"...). In this case, it might help to support
this action using a hot-plug controller: a switch announces the action and an LED signals the state. This
switch is already specified for CompactPCI in the handle and does not have to be invented anew.
Using another well-established standard – SGPIO or SFF-8485 for RAID controllers – this information is
sent to the hot-plug controller. SGPIO is a very simple interface, which transfers binary signals in real
time using four lines. (Cf. Chapter Usage of SGPIO) It is already integrated in many chipsets, meaning
the hot-plug controller does not cause any additional costs. PCI Express per se also supports hot
plugging. The software overhead for supporting the non-transparent PCI Express bridges may not be
underestimated, though.
CompactPCI Serial – Compendium
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Typical Applications
There are a number of quite different applications for which CompactPCI Serial and hot plugging are
perfect. This is why hot plugging is an integral part of CompactPCI Serial. Applications range from a
pluggable hard disk to RAID systems to complex multiple systems.
Hard Disk Drives
For example, imagine a hard disk that has to be quickly exchanged when there is an error. Or a quick
way is required to access data recorded on the hard disk of a data logger. Then there are hard disk RAID
systems, of course, which make it possible to exchange defect disks during operation without impairing
the computer's functionality. All these examples are based on SATA (see also Chapter SATA/SAS for
RAID Systems). A hot-plug controller is needed under certain circumstances, which in most cases is
already integrated in the chipset.
Wireless Systems
Other applications are wireless solutions using Express Cards. These can be integrated on a
CompactPCI Serial peripheral board with Express Card slots and are based on USB and/or PCI Express.
As known from notebooks, you can plug in such cards during operation and can also remove them with
software control. This comes in very handy when servicing is required. A separate hot-plug controller is
not needed.
Multiprocessing
Complex multi-processing is also possible based on PCI Express. CompactPCI Serial allows the
integration of up to nine CPU boards in one system without bridges (with bridges even more, of course).
Communication is controlled centrally via the system slot. This way, very high data rates can be reached
in clustered systems. No special hot-plug controller in the system slot is required, either.
It is much easier to build multiprocessing systems based on Ethernet. In a full mesh network, every card
can directly communicate with every other card without using a switch, so the system slot is not a Single
Point of Failure anymore, i.e. no central point that disrupts the entire system when failing. Special
software is not required either.
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Conduction Cooling
Good thermal management is a decisive factor for the reliability of computers. By a simplified formula, a
computer's life is halved by every temperature step of 10 K (Kelvin). In CompactPCI systems, two basic
types of cooling are common today.
Convection Cooling
The simplest technique is of course natural convection. Since warm air is lighter than cold air, warm air
rises. The flow speed, however, is relatively low. For this reason, you require sufficiently large ventilation
slots and large heat sinks. If you want to operate a CPU board with a power
dissipation of 25 watts at 85 °C, for example, you need a heat sink that covers the space of several slots
in the system.
A smaller heat sink is possible if you accelerate the air using fans (forced air cooling). CPU fans directly
attached to the boards need a lot of maintenance and are not an option because of their lack of reliability.
Instead, the card cages are ventilated as a whole. This works well as long as the heat dissipated per slot
does not exceed a certain extent, and as long as sufficient air flow, which must also be cool enough, can
be guaranteed. The fan tray level below the card cage in turn needs maintenance.
Conduction Cooling
For even more demanding applications, for instance on board an airplane, the so-called conduction
cooling technique is common. Strictly speaking, the term does not even mean the cooling of the boards
but only the transfer of the boards' heat out of the enclosure. To do this, the conductive material is directly
connected to the heat source.
Usually the board is framed by a tailor-made aluminum block, which takes off the heat and directly
transfers it on to the massive enclosure wall over special tensioning wedges called "wedge locks", which
also consist of thermally conductive material. This allows to make the enclosure hermetically tight, and to
give it particular mechanical stability. Of course, the heat must then be transferred away from the outside
of the housing through further measures (e.g., by a fan). Liquid coolers are also suited to do this.
The Approach of CompactPCI Serial
The IEEE standard on which the CompactPCI specification is based defines a special geometry for
boards with conduction cooling, which does not allow cooling a board both by convection and by
conduction cooling without further efforts. As quantities of conduction-cooled boards are rather low, such
boards are especially expensive.
CompactPCI Serial – Compendium
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This is why the CompactPCI Serial specification takes another path. Any convection-cooled card can be
converted into a conduction-cooled card using an individual aluminum block. Saving development costs
for special conduction-cooled boards allows CompactPCI Serial to employ a technology that used to be
expensive on a broad basis.
CCA aluminum frame for CompactPCI Serial assemblies
Standard board inside a CCA frame (left) and conduction-cooled housing (right)
CompactPCI Serial – Compendium
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Physical Addressing
Most modular computers support what is called physical addressing. For CompactPCI Serial this
addressing is particularly important.
Benefits and Pitfalls
Modern serial buses such as SATA, PCI Express or Ethernet support all mechanisms for automatic
configuration to simplify installation of new hardware. For instance, if you connect a hard disk to a
computer using SATA, this drive will be automatically recognized and can be used without any further
configuration.
This advantage can at the same time be a pitfall – just think about a hard disk RAID configuration. In the
case of a failure, you have to find and replace the right drive. This problem is also known with USB
devices. If you connect two USB Flash drives to a computer, you don't know which drive is accessed
where.
Physical Addressing with CompactPCI Serial
This is why physical addressing is a necessity for modular computer periphery. CompactPCI Serial
considers this as well. The system slot is recognized by a special signal (SYSEN), not needing any
additional address information. Even if the base standard does not explicitly describe this, you can of
course expand the eight peripheral slots using suitable bridges. Since a 19-inch card cage
accommodates a maximum of 21 slots, four lines GA[3:0] are provided for geographical addressing to
distinguish these slots. Depending on the backplane position, these lines will be either left open on the
backplane, permanently connected to ground (GND), or connected to ground with a 1-kOhm resistor. This
results in 24 different combinations.
To assure the compatibility of different manufacturers, the CompactPCI Serial specification prescribes the
order in which interfaces like SATA must be implemented on the system slot, if not all eight interfaces can
be supported. If a CPU board is able to support only two SATA channels, for example, these need to be
SATA 7 and 8 (SATA 1 to 6 remaining unsupported).
The base specification defines slots 7 and 8 to be implemented at the very right of the system, if only two
SATA channels are used. (See implementation order in the figure below.) RAID controllers expect the first
drive at address 0. For this reason, the slot at the very right of the system has ID 0 (i.e. all four address
lines GA[3:0] are connected to GND). Accordingly, the neighboring slot to the left has ID 1, and so on.
CompactPCI Serial – Compendium
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System
Slot 0
Fat Pipe Fat Pipe
Perip.
Perip.
Slot 1
Slot 2
Perip.
Slot 3
Perip.
Slot 4
Perip.
Slot 5
Perip.
Slot 6
Perip.
Slot 7
Perip.
Slot 8
PCI Express
USB
Ethernet
SATA
Implementation order of interfaces with CompactPCI Serial
The physical addressing of CompactPCI Serial is compatible with standards like SFF-8485 (SGPIO) for
hard disk RAIDs.
CompactPCI Serial – Compendium
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Mechanics
The Guide Element
In total, the CompactPCI Serial standard defines up to six individual connectors for single Eurocards and
seven individual connectors for double Eurocards.
Depending on the function of the board, a different number of these connectors are assembled. A
peripheral board in 3U format is usually only equipped with one connector at the backplane. This saves
costs. There is a drawback to this, however.
A bigger connector helps to stabilize the board mechanically. Several modular connectors positioned next
to each other are not capable of this. As the main focus of CompactPCI Serial has been usage in harsh
environments from the start, an additional element has been introduced – the so-called guide element –
for guiding, holding and stabilizing the plug-in card on the backplane.
The guide element at the center of the backplane
This way, a 3U assembly is also guided in the middle of the backplane, when only one (the lowest)
connector is assembled. Due to this, the PCB cannot bend. The shock and vibration resistance is higher.
CompactPCI Serial – Compendium
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Connector Usage and Coding
CompactPCI Serial uses so-called AirMax connectors instead of the metric 2-mm connectors of
CompactPCI to link the plug-in card to the backplane. These connectors were chosen for their high pin
density, their excellent transmission behavior with high signal frequencies, and for their mechanical
robustness. They are completely compatible with the IEEE 1101 standard, the common mechanical basis
of CompactPCI and CompactPCI Serial.
Mechanical Fitting of the AirMax Connectors
The pins of the connectors do not protrude through the backplane anymore. With the 2-mm connectors,
the pins of the connectors that were press-fit from the front protruded to the rear side, and a plastic
shroud was put over them from the rear. With the AirMax connectors, this is solved by pressing in
connectors on the backplane from the front and in the rear I/O area from the back. The only prerequisite
to do this is a specific thickness of the backplane.
CPCI-S.0 now defines ground pins between the signal pins following a dedicated pattern. If you look at
the backplane from the rear, this pattern is mirrored. It is an advantage of the AirMax connectors that
there are no special ground pins in the connector. No problems occur when connectors are press-fit from
two sides. Contrary to the common CompactPCI standard, CPCI-S.0 uses receptacle connectors instead
of plug connectors on the backplane, so that twisted pins are a thing of the past.
Segmented Connector Block
The connector has segments. This means that depending on the board's function, not all connector
segments are assembled. Especially connectors P2, P3, P4 and P5 are specified for user-defined I/O on
peripheral cards and offer a total of 360 pins, 120 pins of which are normally defined as GND. If a rear I/O
board is connected at the rear of the backplane, and the I/O functions are customized, the pin-out must
correspond 100% with the front board. If you plug a card with a customized signal assignment into a
wrong slot, the card could be damaged.
CompactPCI Serial – Compendium
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Connector P1 on a standard peripheral card (Ethernet switch) in CompactPCI Serial
P6
3U
P5
P5
P4
P4
P3
P3
P2
P2
P1
Connectors P2 to P5 for user-defined I/O
The layout of the boards and backplane summarizes P2 and P3 as well as P4 and P5 as one hole-pattern
block. As long as the block is completely assembled, you can populate it with any desired AirMax
connectors. There are AirMax connectors with 6, 8 and 10 rows. The connectors are mechanically coded.
A plug connector with 8 rows, for instance, cannot be plugged into a receptacle with only 6 rows.
The standard prescribes that block P2-P3 may be populated by two 8-row connectors, but also with one
6- and one 10-row connector. This makes for three possible P2-P3 configurations: 6-10, 8-8, 10-6. Block
P4-P5 can be populated by 8-6 or 6-8. This makes a total of six different connector arrangements for
customized I/O boards. The corresponding backplane must be populated by the receptacles matching the
I/O board but uses the standard layout.
CompactPCI Serial – Compendium
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Designation
Type
Number of Rows
Number of Walls
Implementation
P0
A
6
4
Optional
P1
A
6
4
Mandatory
P2
B
8
2
Optional
P3
B
8
2
Optional
P4
B
8
2
Optional
P5
C
6
2
Optional
P6
D
8
4
Optional
Standard configuration of the connectors according to CompactPCI Serial specification
This coding option is another alternative to those already provided by IEEE 1101. The connectors are
assembled correspondingly when the board and backplane are manufactured, so that the user cannot
make any mistakes.
Two Card Formats: 3U and 6U
Just like parallel CompactPCI, CompactPCI Serial defines two standard board sizes: single and double
Eurocards. The smaller single Eurocard format (100 x 160 mm, 3U) is particularly suited for compact and
mobile applications. In the fields of servers, telecommunications and measurement, larger card formats
(233 x 160 mm, 6U) may even be an advantage, since the electronic components need more space and
can draw more power.
Compatibility of Formats
The two formats are electrically and mechanically compatible. This means that you can insert 3U boards
also into 6U systems without restrictions. The connector types and even the pin assignment are identical.
The only difference is that for 6U boards an optional connector (P0) was added to amplify power supply
and to provide additional Ethernet channels as an infrastructure bus for server applications.
CompactPCI Serial – Compendium
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However, 3U boards with CompactPCI Serial are not inserted at the bottom, as for CompactPCI, but at
the top, as was the case for the older VMEbus standard. This has two reasons. On the one hand, it is
necessary to amplify the power supply for 6U boards. 3U boards are supplied via the P1 connector. For
6U, this connector needs to be extended.
For EMC reasons and in order not to influence data transfer on the serial interconnects, the power supply
connections have as large a distance as possible to the critical signal paths. It is only logical to place the
additional P0 connector directly next to P1, i.e. below P1. This makes the board grow towards the bottom.
P6
P5
P4
P3
P2
P1
6U
P0
CompactPCI Serial in 6U, extended by connector P0
It is important to note that P0 is the only electrical extension of 6U boards compared to 3U boards. All
features of CompactPCI Serial such as eight PCI Express links, eight full-mesh Ethernet, eight SATA and
eight USB interfaces are available in 3U systems just as in 6U systems.
The second reason for the arrangement from top to bottom is the simple build-up of hybrid boards.
CompactPCI Serial also describes this kind of board. The upper area of a 6U board accommodates the
new AirMax connectors, while the lower area uses the common 2-mm connectors of CompactPCI in their
standard positions.
CompactPCI Serial – Compendium
Page 40 of 68
Power Dissipation and Power Supply
Power dissipation from 12 V is limited to 60 W for 3U boards. 150 W are permitted for 6U. This is
sufficient even to supply power-hungry server chipsets. 150 W is at the same time the physical limit for air
cooling of boards that fill up a 19" rack by 4 HP each. Consequently, a 19" enclosure with 20 6U slots
could generate a theoretical thermal output of 3000 W.
The new AirMax connectors of CompactPCI Serial do not have special power supply pins. Voltage is
supplied using standard connectors suited for signal transmission. The connectors withstand a current
load of 1 A per pin at 85 °C. The mechanical design of the connectors has the contacts placed
individually, without thermal coupling. If one contact connection heats up more than another, the internal
resistance increases, and the current finds its way over cooler contacts. This guarantees that the load is
spread equally over all contacts.
The connector type chosen for P0 is identical with P1. By result, it has 72 contacts and could connect up
to 24 differential signals. Its pins amplify the 12-V supply, but also the 5-V standby supply. A 6U board
may draw a total power of 25 W from the 5 V standby – which is also a concession for server chipsets.
6U only
0 - 06
0 - 05
0 - 04
0 - 03
0 - 02
0 - 01
Pin
6U only
GND
STNDBY
GND
1_UP_A+
nc
-48V_A
A
6U only
+12V
GND
2_UP_A+
1_UP_Anc
-48V_A
B
6U only
6U only
+12V
GND
2_UP_AGND
nc
nc
C
GND
STNDBY
GND
1_UP_B+
nc
-48V RTN_A
D
6U only
6U only
+12V
GND
2_UP_B+
1_UP_Bnc
-48V RTN_A
E
+12V
GND
2_UP_BGND
nc
nc
F
6U only
Power supply pins for 6U boards on connector P0
A total novelty lies in two redundant, isolated 48-V power supplies. They are supposed to support
different telecom standards, and especially solutions such as Power-over-Ethernet (PoE). A 6U board can
provide almost 100 W over the backplane. This hardly has an impact on the thermal balance, because
PoE supplies power for external devices and the 48 V are only controlled.
CompactPCI Serial – Compendium
Page 41 of 68
Ethernet Extension for 6U Cards
Two rows of P0 are reserved for two additional Ethernet channels. These add to the eight channels that
are defined to form a full-mesh network. While these eight channels build up the multiprocessing network
of CompactPCI Serial, the two additional channels can be used for integration into existing CompactPCI
systems based on the PICMG 2.16 standard, but also for system administration.
Parallel CompactPCI systems still use the IPMB, an I²C bus, to do this. However, Ethernet more and
more becomes the standard of choice, here, too. Intel calls this technology AMT (Active Management
Technology). For instance, it can update software even when a system is switched off.
Backwards Compatibility and Sustainability
Especially the different formats and options for signal routing show that modular, industrial computer
systems need flexible concepts. High demands have accompanied the development of CompactPCI
Serial from the start, regarding both existing and future technologies, but also with respect to more
special requirements. The main features in this context are:

compatibility with parallel CompactPCI – PICMG 2.0

compatibility between 3U boards and 6U boards

6U hybrid boards as a bridge between existing systems and the modern serial interfaces

different connector arrangements for customized I/O boards

backplane extensions, e.g., by additional Ethernet channels and Power over Ethernet for newer
technologies
See also Chapters Individual Rear I/O for 3U and 6U and
Application-Specific Backplane Architectures for more on special backplane solutions.
CompactPCI Serial – Compendium
Page 42 of 68
Extension using Mezzanine Cards
With CompactPCI Serial being mechanically based on the IEEE 1101 standard, the standard for 19-inch
systems and Eurocards, mezzanine modules that were developed for these types of boards are also
compatible with CompactPCI Serial. This is particularly important for backwards compatibility to existing
solutions.
The most important types of such mezzanines are PMCs, XMCs and M-Modules. All of these modules fit
on Eurocards. In general, a single Eurocard can accommodate one PMC/XMC or one M-Module, while a
double Eurocard can carry two PMCs or XMCs, or four M-Modules.
Space Requirements
Because of the connector types used for CompactPCI Serial, the space usable for components is a little
bit smaller than with parallel CompactPCI and VMEbus boards. This is why for CPCI-S.0 the P1
connector, being the only connector necessary for peripheral boards, was placed at the lower edge of the
3U board. As this connector is only 13 mm wide and a margin of 2.5 mm each is reserved for support
rails, this leaves a width of 82 mm that is usable for components. A PMC/XMC module with a width of
74.5 mm comfortably fits on the board. Of course, this also goes for an M-Module with 53 mm width.
The same is true for double Eurocards – basically. Since 6U boards expand 3U boards at the lower edge,
connector P1 is located quite at the center of the 6U board. This has no importance for PMC/XMC
modules. Two of these modules find space on a double Eurocard. A maximum of three M-Modules are
possible on a 6U board.
P6
P5
PMC/XMC
P4
P3
P2
P6
P1
P5
PMC/XMC
PMC/XMC
P0
P4
P3
P2
P1
Different types of mezzanines for 3U and 6U boards with CompactPCI Serial
CompactPCI Serial – Compendium
Page 43 of 68
Signal Wiring
The electrical control of mezzanine modules that are based on modern serial interfaces is especially
easy. For XMC modules, you only have to connect the right lines and generate the power supply locally.
Of course, hot-plug support is possible, too.
For modules that are based on older, parallel buses, you need a bridge. PCIe-to-PCI bridges for PMC
modules are available as standard components. For M-Modules you will rather choose FPGA-based
solutions.
Individual Rear I/O for 3U and 6U
The parallel CompactPCI standard already provides the possibility to connect I/O for peripheral slots also
using the backplane. The number of free pins, however, is very limited, especially with 3U solutions.
CompactPCI Serial offers the option of using around 100 pin pairs or 200 single pins even for 3U boards
on connectors P2 to P5. These pins are all embedded into ground pins and are therefore shielded. For
6U boards more than 300 pin pairs or more than 600 single connections are available. Of course, the I/O
signals benefit from the excellent transmission behavior and from high signal frequencies. This allows
achieving data rates of 12 Gbit/s and more for differential signals.
Applications for Rear I/O
Rear I/O on 3U
In the 3U area rear I/O is needed for systems in harsh environments combined with conduction cooling.
I/O signals are normally connected exclusively via rear I/O. Conduction cooling is an effective way for
systems to meet both the thermal and the mechanical requirements, for instance for application onboard
aircraft, trains, or agricultural machines.
Rear I/O on 6U
Rear I/O in the 6U area is very important for many applications. Telecom applications, for example, only
allow front I/O for service purposes. The reason for the use of modular systems based on plug-in cards is
actually the extremely short time that is needed to exchange boards in the case of service. Thanks to the
hot-plug capability of CompactPCI Serial, you do not even have to switch off the power to exchange a
board. Many connections at the front, which would have to be removed before exchange, could
completely undo this advantage. The solution is rear I/O.
CompactPCI Serial – Compendium
Page 44 of 68
Rear I/O in Instrumentation
In measuring and instrumentation there is yet another motivation for rear I/O. A board with an analog front
end often needs an adaptation for measuring values that is different for every application. You can very
well accommodate line drivers on a tailor-made rear I/O adapter. This leaves the front for convenient
status displays.
High Individualization
Rear I/O technology also incorporates two major difficulties. In common CompactPCI systems, all signals
must be led from the front to the backplane. The backplane's connectors route the signals on to the rear
I/O adapter. With parallel CompactPCI the rear I/O and also the PCI bus signals are fixed to 2-mm
connectors. These are not well suited to support the high bandwidths of digital communication or to
handle highly sensitive signals in the field of measurement engineering.
This is why CompactPCI Serial completely does without a definition of the rear I/O connector and even
leaves out the backplane in this area. The individual connector of the front board directly meets the
corresponding connector of the rear I/O board.
This approach has only benefits: Having nothing to do with rear I/O, the backplane becomes smaller and
less expensive. As not all the slots may use rear I/O, because they do not need it, no connectors are
reserved for rear I/O at all.
P6
P5
P4
100 mm
P3
P2
P1
P0
100 mm
Application
Connector
Area
Free rear I/O layout using 6U CompactPCI Serial
CompactPCI Serial – Compendium
Page 45 of 68
While there is still a discussion in the VPX area on how to support optical interfaces, CPCI-S.0 offers a
trouble-free way to make this possible. The front board can directly meet any desired optical connector of
the rear I/O card. The same goes for sensitive signals in the area of measurement engineering. Special
connectors with a high signal-to-noise ratio of the front board can directly contact the rear I/O board.
Again, the CompactPCI Serial concept for 6U rear I/O tries to stay as flexible as possible here. For
applications like optical data transmission or the transmission of highly sensitive signals it offers the
highest possible individualization. At the same time it achieves a very high degree of interoperability. You
might as well employ common 2-mm connectors, for instance for backward compatible hybrid boards.
The rear I/O connector then leads the signals of the parallel PCI bus to the rear I/O adapter. In this
special case, the rear I/O adapter is simply a common CompactPCI backplane.
Application-Specific Backplane Architectures
CompactPCI Serial supports every interface defined in the specification on every backplane slot, i.e.
Ethernet, PCI Express, SATA and USB. This is very convenient, easy to understand and easy to handle.
For certain applications with quantities of more than 50 systems, a customized backplane might be
recommendable. On this backplane, specified interfaces can be wired to specified slots. Theoretically,
such a backplane might have eight slots only for Ethernet, eight slots only for PCI Express, eight slots
only for USB and eight slots only for SATA beside the system slot (i.e. a total of 33 slots). No switches or
bridges are needed for this either, but now the peripheral boards can only be plugged into predefined
slots.
A good example of such a backplane would be one where at least the SATA slots are separated from the
other interfaces. This would result in eight peripheral slots which support Ethernet, PCI Express and USB,
and eight additional slots which can only accommodate SATA boards (hard disks). Such a modular
computer would have eight slots for typical peripheral functions and eight slots for a RAID system, i.e. a
total of 17 slots including the system slot.
CompactPCI Serial – Compendium
Page 46 of 68
Ethernet Full Mesh.
PCIe
,
,S
U SB
ATA
Ethernet Full Mesh.
,
PCIe
U SB
Custom Backplane Extension.
A
SA T
Standard backplane (top) and application-specific backplane with separated SATA slots (bottom)
PICMG
2.0
Periph.
Rear IO
PICMG
2.0
Periph.
Rear IO
PICMG
2.0
System
Slot
PICMG
EXP.0
EXP.0
PICMG
PICMG
PICMG
CPCI-S.0 CPCI-S.0 CPCI-S.0 CPCI-S.0 PICMG
PICMG
System
CPCI-S.0 CPCI-S.0
Perip.
Perip.
Perip.
Slot
Slot
Slot
Slot
Application-specific backplane with two system slots for CompactPCI and CompactPCI Serial
CompactPCI Serial – Compendium
Page 47 of 68
Use in Harsh Environments: EN 50155 as an Example
Just as CompactPCI, CompactPCI Serial is able to meet even the harsh requirements in a train, which we
want to show here with the related standard as an example.
The EN 50155 for the electronic equipment in a train aims at a functionality of 24 hours a day for 20
years, i.e. about 175 000 hours. This is achieved by defining requirements which have to be met in all
imaginable environmental conditions, including the shock and vibration, fog and salt, etc. The standard
also prescribes how to meet fluctuations of the supply voltage and its transients:

Ambient temperature: The EN 50155 requires up to -40 to +85 °C. In addition it defines a thermal
shock of 3 °C/s as a requirement when passing through a tunnel. Because of the extreme
temperatures, the thermal increase rates and the humidity the components and the PCBs have to
resist condensation, which occurs if the temperature rises from values below zero degrees.

Humidity: The EN 50155 prescribes general rules: Relative humidity of an average 75 %, followed by
30 consecutive days with a humidity of an average 95 %. This means that in most cases the
electronic equipment requires waterproof housings or coated assemblies.

Pollution: Depending on the accommodation of the equipment it can be subject to pollution:
conductive dust, oil mist, spray salt and/or sulfur dioxide. Conformal coating and housings with IP
protection class prevent the negative consequences.

Cooling: Forced air cooling should be avoided because it requires increased maintenance work.
Pure convection cooling requires a suitable board and housing design.

EMC: Moving trains are subjected to a multitude of electromagnetic disturbances. The transient/burst
resistance has to be proven according to EN 50121-3-2 and EN 61000-4-4. Resistance against radio
disturbances has to conform to EN 50121-3-2 and electromagnetic radiation to EN 50121-3-2.

Shock and vibration: The EN 50155 describes test methods and limit values which are defined in
EN 61373. Even though the applications listed there stipulate DIN rail mounting, more stable
mounting techniques, which CompactPCI offers, have to be used for high-vibration environments.
For the power supply in railway equipment additional requirements apply such as:

Input voltage: In a system with 110 VDC the input voltage can fluctuate between 77 and 137.5 VDC
without any temporal limit. In addition, the input voltage may vary extremely in a range from 66 to 154
VDC for a period of 0.1 s. In order to meet these extraordinary requirements for the input voltage
range, only power supplies can be used which have been especially designed for use in trains. These
power supplies are available for CompactPCI and thus also for CompactPCI Serial as COTS
products.
CompactPCI Serial – Compendium
Page 48 of 68

Ripple of the input voltage: The direct input voltage from a one-phase or three-phase-generator is
more or less unsmoothed. It can contain significant ripples which may amount to 15 % of the average
voltage and are not kept away from the input filters. In addition the control circuits of the power supply
have to be quick enough to smooth the fluctuations of the input voltage so that they do not occur at
the output.

Input voltage surges: The EN 50155 defines the relation between surge voltage, duration and
source impedance, and higher voltages, which occur for a shorter time and with higher source
impedance. For 110 V, for example, a test with a 1.4-fold overvoltage (154 VDC) for 1 s with a source
impedance of 1 Ohm is prescribed.
Reliability and long availability of the electronics is decisive for railway applications. CompactPCI Serial is
based on CompactPCI and its proven mechanics. The IEEE 1011 standard includes all required
shielding technologies. 3U systems are especially suited for applications in the railway market as they are
extremely space-saving and cost-effective.
Spoiled for Choice: CompactPCI Serial or VPX?
CompactPCI Serial was long in the making. In the meantime, VPX has begun to leave the military niche
and intensifies its efforts to supply civil applications. Both standards are the best that the market has to
offer at the moment regarding robustness and reliability. However, potential customers should consider
carefully in advance for which system features they want or have to spend their money.
There might very well be some industrial or civil applications, where the higher costs of a VPX system are
justified, especially when the NRE purchase costs are too high anyway. In that case, however, enough
time should be scheduled to familiarize oneself with VITA 46, 48, 65-68 and all sub-specifications – while
CompactPCI Serial only consists of a 128-page base specification.
On board level already, higher costs are incurred due to the complex VPX connector which has no
advantages regarding speed, safety or robustness compared to the CompactPCI Serial connector and
even provides fewer signals.
On the other hand, CompactPCI Serial offers no special interconnects such as Serial RapidIO (SRIO) or
Aurora. While SRIO is limited to specific PowerPC and DSP types, however, current x86 processors
support the whole range of PCI Express, Ethernet, USB and SATA – the serial interfaces that
CompactPCI Serial is based on.
CompactPCI Serial – Compendium
Page 49 of 68
Management controller hubs, switches, bridges etc. cost money and make systems more complex, in
other words more expensive. Whatever purpose they have (connecting a slot with the right interface) –
CompactPCI Serial can do completely without, even in a complex multicomputer system. Additional
overhead for software adaptations is not required either with CompactPCI Serial.
The high number of possibilities when configuring VPX systems eventually causes problems with
interoperability which OpenVPX tries to reduce. Nonetheless, the multitude of options makes it almost
impossible to exchange plug-in boards of different manufacturers one-to-one and application-specific
backplanes are the rule rather than standard backplanes.
Thanks to the strictly standardized pin assignment of CompactPCI Serial on the other hand, most
applications, simple or complex, can be built up of standard boards and backplanes at least for the most
part, there are no or very small NRE costs.
As effective cooling is also required from time to time in civil applications such as planes, trains, buses
and mobile machines, CompactPCI Serial also specifies a CCA frame for boards and the corresponding
infrastructure for conduction-cooled systems. In order to save costs, standard assemblies do not have to
be laid out anew for a conduction-cooled environment, which would reduce available space on the PCB,
but instead are equipped with a CCA frame.
The last cost factor: the PSU. For its 5V/12V/48V strategy, VPX also needs more complex PSUs.
CompactPCI Serial defines a single 12V supply and can use COTS PSUs when there is cost pressure.
VPX and CompactPCI Serial – two solid standards, many things in common but two worlds nonetheless:
The costs are what separate them. What is suitable for military and defense applications must not
necessarily be right for cost-conscious markets. CompactPCI Serial is not cheap either, but the
price/performance ratio as a driving factor for the standardization is good.
CompactPCI Serial – Compendium
Page 50 of 68
Migration using CompactPCI PlusIO
Architecture Overview
The CompactPCI specification PICMG 2.0 permits to lead user I/O signals to the backplane beside the
parallel PCI bus. The manufacturers use these user I/O pins to lead these peripheral signals – the
modern serial interconnects – to the backplane. Unfortunately the pin assignment has not yet been
standardized, so that the intercompatibility of the assemblies is lost. Often even boards by one and the
same manufacturer cannot be exchanged among each other. What is more, the 2-mm connector was
originally not developed for transmitting differential signals with a speed of up to 5 Gbit/s.
J
5
J
4
J
3
J
2
J
2
J
1
J
1
Backplane connector J2 with CompactPCI
CompactPCI Serial – Compendium
Page 51 of 68
Standardized Interfaces with CompactPCI PlusIO
An extension to the CompactPCI standard, PICMG 2.30 CompactPCI PlusIO, remedies this. The
extension defines the J2 pin assignment and at the same time introduces a new, 100% compatible
connector, which is also suited for transmission of high frequencies. For this, only a few additional ground
signals are required, so that a high number of interfaces can be led to the backplane:

4 x PCI Express (one lane each)

2 x Ethernet 1000BASE-T

4 x USB 2.0

4 x SATA/SAS
The parallel PCI bus is not changed but is limited to a data bus width of 32 bit. PICMG 2.30 can be used
for both single and double Eurocards. A board that supports CompactPCI PlusIO remains 100%
compatible to the current standard. It can also be used without limitations in existing systems.
Pin Assignment J2
Pin
22
21
20
19
18
17
Z
GND
GND
GND
GND
GND
GND
A
GA4
CLK6
CLK5
GND
2_ETH_D+
2_ETH_D-
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Pin
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
Pin
4_PE_CLK4_PE_CLK+
3_PE_CLK3_PE_CLK+
4_PE_Rx00+
4_PE_Rx003_PE_Rx00+
3_PE_Rx002_PE_Rx00+
2_PE_Rx001_PE_Rx00+
1_PE_Rx00VIO
CLK4
CLK2
CLK1
A
B
GA3
GND
GND
GND
2_ETH_C+
2_ETH_C-
C
GA2
2_ETH_B+
2_ETH_B2_ETH_A+
2_ETH_APRST#
D
GA1
1_ETH_D+
1_ETH_D1_ETH_C+
1_ETH_CREQ6#
E
GA0
1_ETH_B+
1_ETH_B1_ETH_A+
1_ETH_AGNT6#
2_PE_CLK+
DEG#
GND
reserved
2_PE_CLKFAL#
REQ5#
GNT5#
1_PE_CLK+ 4_PE_CLKE# SATA_SCL
reserved
1_PE_CLK- 3_PE_CLKE# SATA_SDO
SATA_SL
1_PE_CLKE# 2_PE_CLKE# SATA_SDI 4_SATA_Rx+
4_PE_Tx00+
4_USB2+
4_SATA_Tx+ 4_SATA_Rx4_PE_Tx004_USB24_SATA_Tx- 3_SATA_Rx+
3_PE_Tx00+
3_USB2+
3_SATA_Tx+ 3_SATA_Rx3_PE_Tx003_USB23_SATA_Tx- 2_SATA_Rx+
2_PE_Tx00+
2_USB2+
2_SATA_Tx+ 2_SATA_Rx2_PE_Tx002_USB22_SATA_Tx- 1_SATA_Rx+
1_PE_Tx00+
1_USB2+
1_SATA_Tx+ 1_SATA_Rx1_PE_Tx001_USB21_SATA_Txreserved
GND
GNT3#
REQ4#
GNT4#
CLK3
SYSEN#
GNT2#
REQ3#
GND
REQ1#
GNT1#
REQ2#
B
C
D
E
F
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
Pin
Pin Assignment J1
Pin 1-25
Standard Assignment
Fixed pin assignment of connector J2 with CompactPCI PlusIO
CompactPCI Serial – Compendium
Page 52 of 68
CompactPCI PlusIO CPU card with new J2 connector (shown individually at the right)
Hybrid Systems as a Bridge between the Standards
A CPU assembly that supports PICMG 2.30 can also be used as a system slot in a hybrid system. A
hybrid system like this provides CompactPCI Express or CompactPCI Serial slots in addition to legacy
CompactPCI slots.
So a small CompactPCI system can consist of a CompactPCI system slot (the CPU board), two
CompactPCI peripheral slots for I/O and fieldbus and two CompactPCI Serial peripheral slots for a hard
disk RAID with hot plug support.
PICMG
2.0
Periph.
Rear IO
PICMG
2.0
Periph.
Rear IO
PICMG 2.0
PICMG
PICMG 2.30
CPCI-S.0
System
Periph.
Slot
PICMG
CPCI-S.0
Periph.
Hybrid backplane with CompactPCI PlusIO and CompactPCI Serial (simplified)
You can find more on hybrid systems in Chapter Hybrid Systems.
CompactPCI Serial – Compendium
Page 53 of 68
PCI Express
CompactPCI PlusIO permits to lead a total of four PCI Express interfaces to the backplane. The "UltraHard-Metric" connectors on the plug-in board permit data rates of up to 5 Gbit/s, traditional 2-mmconnectors being usable on the backplane.
These four interfaces can control four PCI Express based peripheral boards. Every interface is equipped
with one differential receive pair and one differential transmit pair – one lane, with each forming one x1
link. The four PCI Express lines can be a connection to CompactPCI Express or to CompactPCI Serial,
for instance.
Each interface reaches data rates of 250 MB/s with PCIe v1.x or 500 MB/s with PCIe v2.x per direction.
For some applications, however, for example for image processing, these data rates are still not
sufficient. For this reason, the PICMG CompactPCI PlusIO standard allows to "cluster" the four PCI
Express links. This way, the four links with one lane each defined for PICMG 2.30 can also be configured
as two links with two lanes each (x2) or as one link with four lanes (x4). In the last-mentioned case,
theoretical data rates of 1000 MB/s with PCIe v1.x or 2000 MB/s for PCIe v2.x can be reached, but only
with a connected device.
x1
System
Slot
x1
PCIe I/O
PCIe I/O
System
Slot
x2
PCIe I/O
System
Slot
x4
PCIe I/O
x1
cPCI
PlusIO
x1
PCIe I/O
cPCI
PlusIO
x2
PCIe I/O
cPCI
PlusIO
PCIe I/O
PCI Express connection with CompactPCI PlusIO: 4 x1 links, 2 x2 links or 1 x4 link
The PlusIO CPU board imports the configuration via four control lines which are also used to activate the
respective 100-MHz clock that is allocated to a PCI Express interface. No additional lines are necessary.
CompactPCI Serial – Compendium
Page 54 of 68
Ethernet
CompactPCI PlusIO defines a total of two Ethernet interfaces at the backplane. As for PICMG 2.16, the
Ethernet interfaces are based on the IEEE 802 standards for copper cables.
Why BASE-T?
The working group has intentionally decided against special standards for backplanes as were used for
AdvancedTCA or MicroTCA. These special Ethernet standards – 1000BASE-BX (1 Gbit/s) and
10GBASEBX4 (10 Gbit/s) – use two or eight differential pairs, respectively, for transmission and need
special PHYs for this. The PHY is the physical interface, i.e. the interface component between the actual
Ethernet controller and the transmission medium.
As a rule Ethernet connections are implemented redundantly in the AdvancedTCA or MicroTCA
standards. CompactPCI PlusIO, however, uses the common "BASE-T" standards, i.e. 10/100/1000BASET and 10GBASE-T. These are based on four differential connection pairs. Inductive coupling as well as
the simple capacitive coupling is possible. The standards are interoperable without additional software
overhead (autonegotiation). As a rule, from 1000BASE-T on, there is a fault tolerance within the
connection. Modern 1000BASE-T PHYs for example build up at least one 100BASE-T connection if a
wire pair is disturbed. The diagnosis capability of BASE-T PHYs leaves almost nothing to wish for.
BASE-T standards are the most future-safe Ethernet standards. Millions of nodes installed worldwide are
based on them. Research has already begun on an extension to 100GBASE-T – still compatible to
existing installations. The wide-spread use of the BASE-T standards has further consequences: The
PHYs are produced in a very high quantity, so that they are cheap and often already integrated in the
Ethernet controller itself. By now, the power dissipation of the PHYs has become impressingly low (think
about green computing) and the reliability accordingly high.
Possibilities through Ethernet on the Backplane
CompactPCI PlusIO permits building up 3U and 6U multicomputer systems based on Ethernet on the
backplane. As the BASE-T standards also allow line lengths of up to 100 meters, loosely coupled
computers can also be interconnected. Using low-priced standard Ethernet switches complex networks
can also be realized.
CompactPCI Serial – Compendium
Page 55 of 68
Electrical Specification
CompactPCI PlusIO is a standard for CompactPCI system slots, i.e. for CPU boards. Being no backplane
standard, it does not set up rules for backplanes. The standard is limited to the necessary definitions for
the CPU board and how the serial interfaces are led to the backplane.
If you use CompactPCI PlusIO to access the signals via a rear I/O adapter, this is sufficient. If you set up
a hybrid backplane, for example based on CompactPCI Express, to control National Instruments cards at
low cost, it is the responsibility of the backplane manufacturer to bridge the different standards and to
guarantee interoperability.
When defining the rules for the system-slot board in the CompactPCI Serial standard, the approach taken
was to split the electrical tolerances permitted by an interface standard (e.g., PCI Express) between the
CPU board, a possible backplane, and a peripheral board in a "fair" manner. Fair means that the
specified values were divided by three.
In order to make implementation simple, to avoid mistakes and to achieve maximum interoperability, the
electrical specifications of every single standard were turned into clear PCB layout rules. These rules
differ depending on the interface (PCI Express, SATA, USB, Ethernet). For PCI Express the following
rules apply, for instance:

Differential impedance 100 Ohms

The distance between differential pairs and other signals shall be more than 0.4 mm

The pair-to-pair pitch shall be 0.2 mm minimum

Intra pair skew shall be less than 0.1 mm on the system slot board

Trace length shall be less than 125 mm on the system slot board. There shall be a maximum of 2 vias
per line on the system slot board
These clear implementation rules guarantee that the modern high-speed interconnects are really usable,
and that boards of different manufacturers work together under all circumstances.
CompactPCI Serial – Compendium
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Interoperability
CompactPCI PlusIO supports four PCI Express, SATA and USB 2.0 interfaces as well as two Ethernet
interfaces on the backplane. The pins used for this have been left free in the basic PICMG 2.0 standard
for the user I/O of 32-bit systems. PICMG 2.30 can be used for both 3U and 6U systems, if no 64-bit PCI
bus implementation is required.
The signal definition aims at the highest possible interoperability between boards of different
manufacturers. At the same time the standard tries to allow as much flexibility as possible.
Not every CPU board will use all of the new interfaces – also because of the costs. A typical Intel Atom
platform might perhaps only support one Ethernet and one PCI Express. It depends on the
implementation whether SATA can be used. Four USB interfaces are possible if required.
Defined Interface Order
To guarantee maximum interoperability between CPU boards of different manufacturers, CompactPCI
PlusIO defines clearly the sequence in which the interfaces have to be "filled". This makes sure, for
example, that the only PCIe channel of one manufacturer does not collide with a differing assignment of
another manufacturer.
The prescribed order for Ethernet and USB is ascending: 1, 2 and 1, 2, 3, 4; for SATA it is descending: 4,
2x Ethernet
Ethernet 1
Ethernet 2
4x PCIe
PCIe 1
PCIe 3
PCIe 2
PCIe 4
4x SATA
SATA1
SATA 2
SATA 3
SATA 4
4x USB
USB 1
USB 2
USB 3
USB 4
cPCI system slot with
PICMG 2.30
Peripheral slot based
on serial interfaces
Peripheral slot based
on serial interfaces
Peripheral slot based
on serial interfaces
Peripheral slot based
on serial interfaces
3, 2, 1; for PCI Express it alternates: 1, 3, 2, 4.
Maximum implementation of serial interfaces with CompactPCI PlusIO for four CompactPCI Serial peripheral boards
CompactPCI Serial – Compendium
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Ethernet 1
2x PCIe
PCIe 1
PCIe 3
2x SATA
3x USB
USB 1
USB 2
USB 3
cPCI system slot with
PICMG 2.30
Peripheral slot based
on serial interfaces
Peripheral slot based
on serial interfaces
Peripheral slot based
on serial interfaces
SATA 3
SATA 4
Peripheral slot based
on serial interfaces
1x Ethernet
Partial implementation of serial interfaces with CompactPCI PlusIO
Except for SATA the interfaces are filled incrementing – why not the SATA interfaces?
A CompactPCI system using CompactPCI PlusIO can be equipped with up to four of the new serial
CompactPCI Serial slots on the hybrid backplane. These four slots shall even be usable to the maximum
if not all interfaces can be supported by a CPU board. When there are four slots it would be unhandy if all
interfaces were led to the first slot and none to the last. PCI Express and USB are implemented
concurrently in order to enable the use of PCI Express Mini Cards, for example. One slot will often be
needed for a hard disk or an SSD. As only one interface per slot is needed in this case, the interfaces are
filled descending.
Implementation in Real Life
A system based on an Intel Atom SBC might look like this: Ethernet on the backplane controls an
additional computer, a video input card controlled via PCI Express is plugged into the first peripheral slot,
the second slot is equipped with a USB-based RS485 extension, slot 3 supports a Wi-Fi interface – also
USB – and slot 4 accommodates a SATA hard disk.
This shows that the implementation rules have got two advantages:

maximum compatibility between the cards of different manufacturers

optimum exploitation of the resources.
The standard also permits to assign other functions to pins, if necessary. So, if you do not need the
defined four PCI Express, four SATA, four USB and two Ethernet interfaces, you can also lead other
signals to the backplane and still be compatible with the standard. You only need to consider two things:
CompactPCI Serial – Compendium
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
You must keep the implementation order of the interfaces. This means that you cannot simply
assign a different function to any PCI Express interface. Instead, you need to begin with channel 4
and continue in forward direction. With SATA the implementation order is the other way around –
here you begin with the first pin that you can then assign differently.

Connected interfaces which comply with the specification must not be destroyed by user I/O
signals. The standard does not permit, for instance, that the pins are assigned +12 V instead of a
SATA interface, because this could destroy a connected hard disk drive.
For example: Doing without one PCI Express interface and one Ethernet interface, we would like to bring
LVDS graphics to the backplane. According to the implementation rules, we need to reassign Ethernet 2
and PCI Express 4 in this case. The output signals of the LVDS interface are differential, with a relatively
low voltage level. These signals cannot destroy a connected Ethernet device. In the case of PCI Express,
it is better not to drive against a connected device. Consequently, we should avoid using the PCI Express
input pins. The following table shows a possible pin assignment.
Pin Assignment J2
Pin
22
21
20
19
18
17
Z
GND
GND
GND
GND
GND
GND
A
GA4
CLK6
CLK5
GND
LVDS_D+
LVDS_D-
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
LVDS_CLKLVDS_CLK+
3_PE_CLK3_PE_CLK+
free
free
3_PE_Rx00+
3_PE_Rx002_PE_Rx00+
2_PE_Rx001_PE_Rx00+
1_PE_Rx00VIO
CLK4
CLK2
CLK1
B
GA3
GND
GND
GND
LVDS_C+
LVDS_C-
C
GA2
LVDS_B+
LVDS_BLVDS_A+
LVDS_APRST#
D
GA1
1_ETH_D+
1_ETH_D1_ETH_C+
1_ETH_CREQ6#
E
GA0
1_ETH_B+
1_ETH_B1_ETH_A+
1_ETH_AGNT6#
2_PE_CLK+
DEG#
GND
reserved
2_PE_CLKFAL#
REQ5#
GNT5#
1_PE_CLK+ 4_PE_CLKE# SATA_SCL
reserved
1_PE_CLK- 3_PE_CLKE# SATA_SDO
SATA_SL
1_PE_CLKE# 2_PE_CLKE# SATA_SDI 4_SATA_Rx+
free
4_USB2+
4_SATA_Tx+ 4_SATA_Rxfree
4_USB24_SATA_Tx- 3_SATA_Rx+
3_PE_Tx00+
3_USB2+
3_SATA_Tx+ 3_SATA_Rx3_PE_Tx003_USB23_SATA_Tx- 2_SATA_Rx+
2_PE_Tx00+
2_USB2+
2_SATA_Tx+ 2_SATA_Rx2_PE_Tx002_USB22_SATA_Tx- 1_SATA_Rx+
1_PE_Tx00+
1_USB2+
1_SATA_Tx+ 1_SATA_Rx1_PE_Tx001_USB21_SATA_Txreserved
GND
GNT3#
REQ4#
GNT4#
CLK3
SYSEN#
GNT2#
REQ3#
GND
REQ1#
GNT1#
REQ2#
F
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
Possible pin assignment compatible with CompactPCI PlusIO with LVDS on connector J2
CompactPCI Serial – Compendium
Page 59 of 68
Hybrid Systems
Using CompactPCI PlusIO
The first that comes to mind when thinking of building up hybrid systems is CompactPCI PlusIO (PICMG
2.30). Here, the system slot CPU supports both the parallel CompactPCI standard (PICMG 2.0) and the
new CompactPCI Serial standard (PICMG CPCI-S.0). Hybrid backplanes from different manufacturers
enable configuration with peripheral slot boards on the left and on the right of the system slot board. Up to
seven parallel and a maximum of four serial boards are supported – without a bridge.
I/O
I/O
cP
Se r C I
i
Pe r a l
.
I/O
I/O
I/O
cPCI
PlusIO
cPCI
Per.
cPCI
Per.
cPCI
Per.
cPCI
Per.
cPCI
Per.
cPCI
Per.
cPCI
Per.
cPCI
Syst.
I/O
I/O
I/O
I/O
cPCI
Serial
Per.
I/O
CI
cP rial
Se er.
P
I/O
c
Se PC
Pe ria I
r. l
Hybrid system with CompactPCI PlusIO CPU, and CompactPCI and CompactPCI Serial peripheral boards – schematic
This way, a cost-effective migration is possible, because the usage of future-oriented and standardized
data transfer based on CompactPCI Serial is guaranteed even when already integrated CompactPCI
components are used.
The Important Role of CompactPCI PlusIO
CompactPCI PlusIO’s importance lies in a simple fact: because it has been so successful, CompactPCI
has a large installed base, and to abandon this structure in favor of a completely new system is of no
benefit to anyone – manufacturer, developer or end user.
The CompactPCI PlusIO standard provides for the addition of high-speed serial communication, while
preserving PCI bus connectivity and maintaining the mechanical parameters of the original CompactPCI
standard. The result is a practical migration path for users who require the added capabilities, without
CompactPCI Serial – Compendium
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disrupting continuity for those aspects of their applications where original CompactPCI hardware
components still perform acceptably.
CompactPCI: an Evolving Standard
The development path of CompactPCI affirms that the standard is able to continually evolve, while
maintaining the original mechanics. This attribute has enabled updated versions to remain compatible
with legacy systems, and ensures that the extensive installed base of CompactPCI systems remain
viable, relevant and cost-effective within the many industries using CompactPCI as well as those that can
now benefit from the high-speed serial interfaces.
Areas with the most evolution are primarily seen where the systems’ performance and ease-of-use, such
as multi-computing networking, increased reliability and hot-swap functionality count.
CompactPCI is one industry standard that will not easily fall victim to the fate that “all good things must
come to an end,” which has proven true time and time again in computing technology. The ratification of
PICMG 2.30 and PICMG CPCI-S.0 (CompactPCI Serial) has in all probability delayed any possible
obsolescence of CompactPCI for another 15 years or more.
Hybrid Possibilities using CompactPCI PlusIO
The CompactPCI PlusIO hybrid system offers the perfect connection between parallel and serial
architectures, and a gradual transition from old to new. This type of solution offers the ability to
incorporate existing CompactPCI I/O cards within an installation accommodating serial I/O connections
that help maximize the value of the user’s investment in CompactPCI hardware while providing the
flexibility to satisfy increased operational demands.
It is not necessary to completely replace an existing system in order to upgrade it to the latest
technological standard – nor is it necessary to scrap successfully proven components. Even
implementation is surprisingly easy and cost-efficient due to compatibility with much of the existing
hardware.
In its simplest application, the installation of a new CompactPCI PlusIO SBC into an existing system slot
can integrate up to seven parallel I/O boards and four serial I/O boards (CompactPCI Serial) in the same
configuration.
CompactPCI Serial – Compendium
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PICMG
PICMG
PICMG
PICMG
PICMG
PICMG
PICMG
PICMG
2.0
2.0
2.0
2.0 & 2.30 cPCI Serial cPCI Serial cPCI Serial cPCI Serial
peripheral peripheral peripheral system peripheral peripheral peripheral peripheral
slot
slot
slot
slot
slot
slot
slot
slot
Ethernet (optional)
legacy CompactPCI 32bit
P2 (rear I/O) connector
P2
pinout
PICMG
2.30
CompactPCI Serial Slots
CompactPCI area for rear I/O
(optional)
legacy CompactPCI 32bit P1 connector
CompactPCI Serial base connector
Hybrid system with a CompactPCI PlusIO CPU – example backplane
But whatever the eventual configuration, CompactPCI PlusIO remains true to the mechanical
requirements of the original CompactPCI standard – including identical board and backplane dimensions,
identical front panels and identical hot-plug mechanics. Also, since CompactPCI PlusIO needs no switch
boards in the system, and the high-speed connector is low cost, it is an exceptionally money-saving
option.
Hybrid backplane in a 19“ system
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Direct Connection between CompactPCI and CompactPCI Serial
But what if none of the standard hybrid backplanes is suitable for the new application and/or more than
four serial peripheral boards are needed and the (first) quantities are too small for the development of a
customized backplane?
In this case, the two worlds – CompactPCI Serial und CompactPCI – have to be connected in a different
way. For this, one board pair is used. One board is the interface from CompactPCI Serial to CompactPCI
and is plugged into a peripheral slot of the CompactPCI Serial backplane. The second interface board
replaces the system slot CPU on the CompactPCI backplane and is connected to the first interface board
in the CompactPCI Serial system via a cable at the front panel.
Interface cards for CompactPCI and CompactPCI Serial connect the two systems
CompactPCI Serial – Compendium
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The new system slot board in the CompactPCI system is equipped with a PCI Express to PCI bridge, the
communication over the cable is based on a PCI Express x1 link. As both standards are compatible to the
19" mechanics, the solution can be accommodated in one rack. On the other hand PCI Express enables
cable lengths of up to 7 m so that two racks can also be coupled loosely.
optional
PCI Express x1
PCIe to
PCI
Bridge
J
2
cPCI System
Slot
PCI
J
1
PSU
Cable
PCI Express x1
Buffer
PSU
cPCI Serial
Peripheral Slot
PCI Express x1
P1
Direct connection between CompactPCI and CompactPCI Serial and separated backplanes
If – for larger volumes – the development of a customized backplane is profitable, the PCI Express based
connection of CompactPCI Serial to CompactPCI can be done via rear I/O. This means that you only
need the second interface board, which is plugged into the system slot of the CompactPCI side.
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Perspective
There are good reasons for using CompactPCI Serial:

It is the logical extension of the existing CompactPCI technology.

Many suppliers have already included CompactPCI Serial into their product range.

Thanks to the higher data throughput and the fast serial connections CompactPCI Serial offers
additional application possibilities.
So much for the levelheaded arguments. There's actually more to CompactPCI Serial than bringing a new
technology to the market, because what's behind it is the impressive success story of one industry
standard: CompactPCI.
CompactPCI has already proven itself in the field for the last 15 years. The 19" system technology with its
typical design and interface assignment is to a large extent known in the industrial market. The design
and structure of the boards, as well as front and rear I/O options are widely accepted by users.
This is why CompactPCI Serial consequently follows up on its parallel predecessor. Its high demand is to
make modular systems simple, robust, flexible and inexpensive – while the mechanics remain 100%
compatible with CompactPCI 2.0. Industrial computers do not follow fashion trends but hard facts, data
and requirements. A technology that simplifies the building up of embedded computer systems, that
allows the integrator to concentrate on his technical requirements while granting continuity and futuresafety hits the nail on the head in the industrial arena.
Wide Support by Suppliers
In order to establish a new technology on the market, the potential users also need choices – both when
choosing a suitable supplier and through a large product range. The support of CompactPCI Serial by a
large number of suppliers on the one hand results in a high degree of innovation and a wide product
range. On the other hand, it creates price competition.
This way, the user can choose between different products and the technical support of the respective
suppliers. Thanks to this network it is possible to combine products of different manufacturers to build up
a system or a special application.
CompactPCI Serial – Compendium
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Extended Fields of Application
By embedding serial interfaces into a system, new application possibilities open up, which could not be
implemented anymore using the traditional parallel CompactPCI architecture. CompactPCI Serial
supports serial communication, a high data transfer rate and high-performance graphics and can even be
operated in combination with parallel CompactPCI in hybrid systems. This means that existing systems
and applications do not have to be replaced completely, but can be extended by the new technology with
high data throughput.
Everything Falls into Place
CompactPCI Serial is not a technology caprice. Several vendors together and with attention to detail have
created a standard for the future and pay highest tribute to its predecessor CompactPCI. The concept
was made not for the next three or five years, but for a minimum of ten years. After the initial introductory
years, both the products and the first projects in real-world applications give proof that this technology can
and will take hold.
CompactPCI Serial as a stand-alone architecture and as an extension of existing technologies offers the
best prerequisites for an efficient implementation of your requirements. A whole network of suppliers with
a wide variety of products is there to support you.
CompactPCI Serial – Compendium
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Abbreviations
AMC
Advanced Mezzanine Card, also: AdvancedMC
AMT
Active Management Technology
ANSI
American National Standards Institute
ATCA
Advanced Telecommunications Computing Architecture, auch: AdvancedTCA
CCA
Conduction-Cooled Assembly
IEEE
Institute of Electrical and Electronics Engineers
IPMB
Intelligent Platform Management Bus
IPMI
Intelligent Platform Management Interface
MicroTCA
Micro Telecommunications Computing Architecture, also: µTCA
NAS
Network Attached Storage
NRE
Non-Recurring Engineering
PCI
Peripheral Component Interconnect
PCIe
PCI Express
PHY
Physical Layer
PICMG
PCI Industrial Computers Manufacturers Group
RAID
Redundant Array of Independent Disks
SATA
Serial Advanced Technology Attachment, also: Serial ATA
SAS
Serial Attached SCSI
SBC
Single-Board Computer
SGPIO
Serial General Purpose Input/Output
SRIO
Serial RapidIO
SSD
Solid-State Drive
CompactPCI Serial – Compendium
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STD Bus
"Simple to Design" Bus
VITA
VMEbus International Trade Association
VMEbus
Versa Module European Bus
VPX
Versatile Performance Switching
www.men.de
www.men-france.fr
www.menmicro.com
October 2015
Copyright © MEN Micro Inc. / MEN Mikro Elektronik GmbH / MEN Mikro Elektronik SAS
All rights reserved.
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