Keysight Technologies PXI Interoperability— How to Achieve Multi-Vendor Interoperability in PXI Systems

Keysight Technologies PXI Interoperability— How to Achieve Multi-Vendor Interoperability in PXI Systems
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Keysight Technologies
PXI Interoperability—
How to Achieve Multi-Vendor
Interoperability in PXI Systems
Application Note
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2 | Keysight PXI Interoperability - Application Note
PCI communications
Table of Contents
Introduction to PXI interoperability
PCI communications
Mechanical and electrical compatibility
PXI hardware
Module sizes
Chassis and controllers
Tips to improve interoperability experience
Related information
Introduction to PXI interoperability
Test system developers generally require a large variety of components to meet system needs, and at times they are sourced
from different suppliers. The system developer must have confidence that these components will work well together. Mechanical,
electrical and software aspects need to be compatible to ensure
successful system operation. That is one of the primary goals of
standard organizations. If standards are carefully written, the resulting specification will promote compatibility between products
and suppliers. In the case of PXI instruments there are multiple
standards organizations that come into play. These organizations
define PCI bus connectivity, chassis and timing synchronization
This application note starts with a detailed look at PXI specifications and discusses its impact on interoperability. It then
discusses PXI hardware and how to select modules, chassis and
controllers to ensure compatibility. PXI software, including tools
such as Keysight Command Expert (KCE) and National Instruments Measurement & Automation Explorer (NI-MAX), are also
discussed because software plays a large role in the overall
compatibility of system components. With the goal of a smooth
implementation of PXI multi-vendor based solutions, hints and
tips are included throughout this note.
PCI bus electrical and signaling attributes are developed and
managed by the PCI Special Interest Group (PCI-SIG). PCI and
PCIe® electrical bus structures used in PXI are based on the
Personal Computer PCI bus and common chipset and signaling
methods are used. Since the PCI bus is ubiquitous worldwide, a
high level of interoperability is assured by the millions of engineering hours invested over the last two decades. PXI leverages
these investments resulting in robust connectivity between modules and chassis and an easy to use solution.
The engineering investments made in PCI technologies have
resulted in a robust boot and messaging process. At PC boot time
the PC BIOS discovers PCI hardware on the bus (including PXI
modules) and the operating system will assign resources including
memory and interrupt. This process is known as enumeration.
Mechanical and electrical compatibility
Upon its initial introduction 1992 the PCI bus was recognized
as being a robust high speed computer interface. It performed
very well in standard business applications, and it soon became
apparent it also would work well in industrial applications. The
PCI Industrial Computer Manufacturers Group (PICMG) leveraged
the PCI bus capabilities, and in 1997 it introduced a specification for an industrial grade enclosure known as CompactPCI®
(cPCI). Compact PCI was a very good mechanical platform to
build from and was quickly adopted in industrial applications.
The mechanical slot spacing, connector placement and pinouts are all defined as part of the cPCI specification. Standard
mechanical dimensional constraints and strict tolerances allowed
smooth insertion of modules into chassis using common installation levers. These attributes combined with standard connector
definitions and pin-outs allow various suppliers to begin sourcing
interchangeable cPCI solutions. However, cPCI had no provisions
for timing and synchronization features necessary in instrumentation applications. This is where the PXI stepped in and provided
instrumentation specific features.
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3 | Keysight PXI Interoperability - Application Note
PXI specification ties it all together
The PXI specification is defined and managed by the PXI Systems
Alliance (PXISA). This specification builds on the PCI and cPCI
specifications by defining instrumentation specific attributes
including timing and synchronization features. A cPCI chassis and
a PXI chassis look very similar and cPCI modules can be used
in PXI chassis. In this application note, we discuss how the PXI
specification provides a framework for multi-vendor interoperability. Figure 1 shows the hierarchy of the PXIe specification. Notice
multiple sections where CompactPCI and PCI bus attributes are
It is important to remember there are two variations of PCI bus
structures—the original parallel PCI style (including both 32 and
64-bit structures), and the newer PCIe based serial structures.
Both bus structures have been worked into the PXI specification.
The original parallel PCI implementation is known as PXI-1 while
the newer serialized PCIe style is known as PXIe. PCIe (and hence
PXIe) provides a significant improvement in data bandwidth as
well as other features such as point to point messaging which are
important in high-end instrumentation applications. Engineers
upgrade to PXIe primarily for higher-speed communications features, in addition to improved timing and synchronization built on
new high speed differential connectors
The PXIe additions also included provisions for PXI-1 backward
compatibility. PXI-1 backward compatibility is critical since there
are many existing PXI modules that are designed based on the
older 32-bit parallel version of PXI. The intent is to allow re-use of
those designs without having to modify the basic design including
the PCB layout. However, a connector modification is needed,
and this is discussed in the next section.
PXI Express PCI Express® eXtensions for
Instrumentation Hardware Specification
PXI Express
PXI-1 and
PXI Express
PXI-1 and
Slots and
System timing
PCI Express
Differential 100
MHz clock
IEC connectors
Differential point
to point triggers
Triggers ref
clock local bus
PXI-1 slots and
hybrid slots
Figure 1. PXIe specification hierarchy (from PXIe specification) 1.
variable clock
Single ended ref
clock triggers
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4 | Keysight PXI Interoperability - Application Note
PXI hardware
Module sizes
PXI modules come in two sizes - referred to as 3U and 6U. The
most popular size is the 3U, which is 100 mm x 160 mm. There
are over 1000 PXI modules currently available—the majority which
are shipped in the 3U format and use 32-bit PCI bus for communications. Both mechanically and electrically 32-bit, 3U PXI-1
modules are well established and a large variety of modules are
currently in production. We’ll focus mostly on the 3U form factor
for the remainder of this discussion.
Figure 2 shows a 3U PXI-1 module. The connections for both
communications and other functions are routed through connectors J1 and J2 to the chassis backplane. J1 is used for 32-bit PCI
communication connections, and it provides all the signals necessary for 32-bit PXI modules to communicate to the controller. J2
contains the extra upper 32-bits in the event a 64-bit PCI version
is supported, as well as additional PXI specific connections to
support timing and synchronization.
PXIe uses the newer high speed PCIe serialized version of the PCI
bus that provides an improvement in data bandwidth. To support
the high speed PCIe signals, a newer differential style connector
must be used to connect to the chassis backplane. The standards
organizations were challenged to develop a method to route the
high speed PCIe connections to PXIe modules that would also be
compatible with the original PXI-1 connector footprint.
Above the red dotted line in Figure 2, critical PXI-1 signals including timing, triggering and local bus lines are routed to the J2
connector. Below the red line, connections are made for upper
bits for 64-bit PXI-1 modules and little used PXI local bus connections.
The standards organization decided to reutilize the lower portion
of J2 to route the high speed PCIe connections. In order to support PXIe connector J2 would be modified:
(1) The top section would remain the same to support
legacy PXI-1 triggering, and
(2) The bottom portion of J2 would be re-assigned for
use for the high speed PCIe communication signal routing.
With this re-assignment, two new styles of chassis peripheral
slots were created: PXIe and Hybrid PXI slots.
Figure 2. PXI-1 3U PXI module. Notice J1 is used for 32-bit parallel PCI connections 1.
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PXI hardware
Connectors (continued)
Figure 3 shows how an existing PXI-1 PCB layout can be redesigned or re-worked using a shorter connector to fit into a hybrid
slot and how that same slot can also accommodate a PXIe module.
Figure 3. Legacy PXI-1 vs. hybrid and PXIe style
modules and slots 1.
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6 | Keysight PXI Interoperability - Application Note
PXI hardware
Connectors (continued)
Figure 4 shows views of these two styles of modules. Figure 4b
shows the lower connector with differential connections. This
differential connector is special to support the high speed signals
required for PCIe (up to 5 Gbit/sec). The advantage of this new
connector configuration is that existing PXI-1 designs can be reconfigured by their manufacturer by simply replacing the larger
J2 connector footprint with the shorter PXI-1 hybrid slot compatible connector (Figure 4a). This allows older module designs to be
used in new PXIe chassis that contain hybrid style slots.
One aspect to be aware of, is that older PXI-1 modules with both
J1 and J2 installed cannot be plugged into a PXI-1 hybrid style
slot since the J2 connector will mechanically interfere with the
new PCIe connector. If you have the old PXI-1 modules on-hand,
visually inspect the connectors to be sure if they are compatible. In the event they are not, some PXI module suppliers offer
a modifications service to remove the J2 connector and replace
with the shorter XJ4 connector. The good news is the majority of
PXI-1 modules shipped today are shipped in a hybrid compatible
format. To be sure, before purchasing new PXI modules verify
with the module supplier that it is available in either hybrid or
PXIe format.
Figure 4a. PXI-1 hybrid compatible style.
Figure 4b. PXIe connector style.
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7 | Keysight PXI Interoperability - Application Note
PXI chassis and controllers
PXI controllers
As mentioned earlier, the advantages of PXIe compared to PXI1include significantly higher throughput, point-to-point messaging and improved triggering and synchronization. As such, in
the future you will see more instruments in the PXIe format. To
support both the older PXI-1 and the newer PXIe style modules, it
is helpful to have many hybrid compatible slots in the PXIe chas-
PXI controllers or personal computers (PC), can be located either
outside the PXI chassis or embedded in the PXI chassis (installed
into the chassis slot 1). First, let’s discuss external controllers.
During the early years of PXI external controllers would connect
to the chassis using proprietary communications interfaces. As
the PCIe communications protocol was developed, a PCIe physical layer that could extend beyond the controller was also developed. This means that the PCIe bus itself can now be extended
directly between the controller and the chassis. No longer is a
proprietary interface required. This is an advantage since an all
PCIe based communications bus using standard COTS connectors, cables and chipsets greatly simplifies the communications
bus design and use. However, there are some caveats. PCIe driver
characteristics, clocking and the BIOS used in the controller are
all important characteristics to note.
Interoperability Hint
Select a chassis with many
hybrid slots to provide slots for both
PXI-1 Hybrid and PXIe style modules
sis. For maximum flexibility and interoperability, select a chassis
with all hybrid slots to provide slots for both PXI-1 Hybrid and
PXIe style modules. The Keysight M9018A chassis has been
designed to maximize the number of hybrid slots. If you are using PXI-1 modules with the J2 connector, select a chassis with
PXI-1 slots or make sure you can convert these to PXI-1 hybrid
In tower and desktop controllers or PC the PCIe bus is typically
accessed via a PCIe connector located on the PC motherboard,
and routing the bus externally using a PCIe plug-in adaptor card.
Keep in mind when controlling a PXIe chassis there may be a long
cable connecting the controller to the chassis. The long cable will
impact signal loading and can inversely impact the eye opening
for the high speed PCIe data. For optimal driver capabilities,
equalization can be applied to the PCIe drivers improving the
ability to drive long cables. Clock jitter can also impact PCIe
communications, especially at the high PCIe Gen 2 rates. PCIe
adaptor cards are available that can isolate and then re-generate
a lower jitter PCIe clock to be used when decoding the PCIe
Interoperability Hint
Figure 5. Keysight M9018A 18-slot chassis with 16 hybrid slots.
If using an external controller, choose a
PCIe adaptor card optimized for driving
long PCIe lines and provides clock isolation
with low clock/data jitter.
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PXI chassis and controllers
PXI controllers (continued)
To address PCIe signal drive and clock jitter concerns, select a
proven PCIe adaptor card product. For example, the Keysight
M9048A PCIe adaptor card has been engineered to provide PCIe
drivers optimized to drive external PCIe cables. In addition the
M9048A provides clock isolation also improving high speed PCIe
data transmission. The M9048A clock isolation circuits are engineered to keep clock to data jitter extremely low, improving the
timing margins at the PCIe receivers.
The enumeration process as previously described can also be
impacted by the controller BIOS. To enumerate a full sized PXIe
chassis, 30 or more PCI end points must be enumerated during
the PC boot process. The number of PCI endpoints supported
by BIOS in some business grade controllers (PCs) may be
limited since business applications typically only need a few PCI
Interoperability Hint
When using a PXIe chassis with embedded
controller be aware that the controller
must also be a PXIe style controller.
An embedded controller, specifically designed for use in slot 1 of the
PXI chassis, can be used to control PXI instruments. If you are
considering using an embedded controller it is important to note
that the backplane connections for PXI-1 style controllers are different than PXIe controllers. PXI-1 controllers route the
32-bit parallel PCI bus while PXIe controllers route the high
speed PCIe signals. The connectors are physically different and
as such a PXI-1 controller cannot be used in a PXIe chassis.
When selecting an embedded controller to use in a PXIe chassis
keep in mind the controller must also be a PXIe style.
Interoperability Hint
If using an external controller select one
that has been pre-tested to verify BIOS
and signal characteristics are suitable for
full enumeration of PXIe chassis.
To reduce risk of selecting a controller or PC that is not capable,
Keysight has pre-tested popular PC controllers to verify operation. If you plan to use an external controller it is best to select
one that has been pre-tested to verify BIOS are suitable for full
enumeration of the PXIe chassis. For more information see the
Tested Computer List (publication number 5990-7632EN).
Figure 6. Keysight M9037A PXIe embedded controller.
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9 | Keysight PXI Interoperability - Application Note
Software is a critical component to consider when designing
automated test systems. You may be concerned about mixing
software, modules and chassis from different suppliers or selecting one IO library over the other. This section will address these
questions and discuss software aspects of controlling your PXI
PCI is the primary communications path for PXI instruments.
Just as the PCI electrical specifications provide a framework for
electrical connectivity, the PCI device driver provides a common framework for software access. For improved usability and
supportability, the driver stack usually is partitioned into multiple
layers. Figure 7 shows the software stack used to communicate
to Keysight PXI modules.
Application software access to a module is always provided
through the instrument driver. For Keysight products, this consists
of an IVI driver, VISA driver and kernel driver. These three layers of
software form a tightly coupled group that work together.
For software to successfully communicate to a PXI module the
complete software driver stack must be installed and the driver
needs to correctly be associated to the module hardware. The
driver is associated to the hardware when the PC boots up. At
PC boot, the BIOS will discover PCI module on the bus and places
information from the module into a file location called Extended
System Configuration Data (ESCD). Memory, bus addresses and
IRQ’s are assigned and stored into the ESCD. Next, the Microsoft
Windows Plug&Play manager will process that information and
create Instance ID’s, associate drivers to the module and finally
archives that information into a Windows Plug&Play manager
information file.
IVI driver
kernel driver
work together
and form tightly
coupled group
VSA library
Kernel driver
VISA driver installation
Module IVI installation
Figure 7. Software stack used to access Keysight PXI modules.
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10 | Keysight PXI Interoperability - Application Note
The end result of this process can be observed in the Windows
Device Manager. Figure 8 shows a fully enumerated M9018A
chassis with Keysight Technologies, National Instruments and
Pickering PXI modules present.
Viewing the PCI devices using Windows Device Manager is a good
check of the status of the modules and the drivers. This view tells
us if the modules were successfully enumerated during boot time
and the instrument kernel drivers are present and associated with
the hardware or not. These are the first and most important steps
to achieve software access to your instruments.
At this point it is always helpful to use the vendor provided soft
front panel (sometimes known as test panel) to verify communications to the module. The vendor’s SFP is a low level software
tool that can be used to verify the health of your installation and
module hardware.
Interoperability Hint
Use the Windows Device Manager to
determine if PXI modules are present on
the PCI bus and if a driver is associated to
the instrument.
Instrument drivers, I/O libraries, ACE and NI-MAX
In the previous section we discussed how critical it is to have an
instrument software driver. For Keysight products the instrument
driver is made up of multiple layers as we showed in Figure 7. The
layers in tan are installed with the IVI driver installation, and are
unique to the PXI module. The layer in blue is the VISA layer and
it is installed with the Keysight I/O libraries. The VISA installation
is common to all Keysight PXI modules. These software layers
are separated this way for improved usability and supportability.
Because of these software layers the driver installation requires
both the Keysight I/O libraries and the module IVI driver. The Keysight I/O libraries can be found at
and individual IVI drivers can be found at
drivers. Search for the specific PXI module number.
Figure 8. PXI instruments as they appear in Microsoft Windows
Device Manager.
With the I/O libraries and driver installations come other tools
that are helpful when developing test programs. For example, the
Keysight Connection Expert (KCE) is installed with the Keysight
I/O libraries. KCE can be used to inspect your instrument installation. It will help you visualize the contents of the chassis and
inspect the driver revisions. Also, included with the instrument
driver installation is a soft front panel, which helps verify initial
communications and is useful when turning on the system.
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11 | Keysight PXI Interoperability - Application Note
Instrument drivers, I/O libraries, ACE and NI-MAX
considerations (continued)
Installation for 3rd party drivers, such as those from National
Instruments, is similar to the Keysight driver installation process.
The process includes installation of both the I/O libraries (NIVISA) as well as individual PXI module drivers. Details will vary
depending on the PXI module provider, but some of the installations also include tools similar to what the Keysight installations
provide. For example when installing NI-VISA the Measurement
& Automation Explorer (MAX) is also included. MAX is similar to
ACE in that it gives you the ability to inspect your module installation. Also, MAX provides some data management and IVI configuration store editing tools which are useful.
Figure 10. M9018A with various PXI modules viewed with KCE.
Figures 10 and 11 provide example views of the same system
displayed by Keysight Connection Expert (KCE) and National
Instruments MAX. They both show the chassis and modules
within the chassis. Chassis slot information is very helpful when
configuring large systems, and it is also helpful to use tools like
KCE and MAX.
The resource descriptor or PXI address is an additional important piece of information provided by KCE and NI-MAX. These
are used by the IVI driver to access the module. In the case of
Keysight PXI products, you pass the VISA PXI address. This is the
address that is shown in parenthesis in Figure 10 (VISA address
format is = PXIxx::yy::zz::INSTR). In the case of NI PXI products you generally use the PXI resource descriptor as shown in
quotation marks in Figure 11. It is important to keep in mind that
you set the VISA aliases or descriptor using the corresponding
supplier’s tool—use Keysight KCE to assign names for Keysight
devices and use NI-MAX to assign the resource descriptor names
for NI device.
Figure 11. M9018A with various PXI modules viewed with NI-MAX.
Interoperability Hint
Use Keysight Connection Expert (KCE)
and/or NI Measurement and Automation
Explorer (MAX) to view PXI modules in
the chassis.
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12 | Keysight PXI Interoperability - Application Note
The key interoperability points we’ve made in this application note
will help you achieve a smooth implementation of multi-vendor
PXI configurations. Here are a few tips:
– Select PXI modules are PXI hybrid slot compatible (older
PXI-1 modules may not be).
– If using an embedded controller ensure consistent form
-- PXIe chassis require PXIe controllers
-- PXI-1 chassis require PXI-1 controllers.
– To support future needs select a chassis with a large number
of hybrid slots to support for both PXI-1 hybrid and PXIe style
– If using an external controller select one that has been pretested to verify BIOS has enough bus numbers allocated to
enumerate a large PXIe chassis. See:
– If using an external controller, choose a PCIe adaptor card
optimized for driving long PCIe lines, and provides clock
isolation with low clock/data jitter.
– Insure a complete driver stack is installed including both VISA
software libraries and PXI module drivers.
– Use Microsoft Windows Device Manager to determine if PXI
modules appear on the PCI bus and if a driver is associated to
the instrument.
– Use the module Soft Front Panels as a quick check of successful hardware and software installation.
– If using VISA alias or resource descriptors, use the corresponding suppliers tools for setting: Use Keysight Connection
Expert for Keysight modules and National Instruments MAX
13 | Keysight
PXI Interoperability - Application Note
or NI modules.
PXI chassis, controllers and instrumentation are based on standards maintained by the PCI-SIG, PICMG and PXISA organizations. These standards provide both the user and vendor several
advantages including leveraging components and engineering
investments made for high volume PC businesses. Common PCI
bus inspection tools such as Microsoft Windows Device Manager
give an independent verification of the PXI module driver installation and operation.
Instrument suppliers that adhere to these standards go a long
way to ensuring multi-vendor interoperability. However, there are
some aspects to keep in mind when configuration PXI systems.
PXIe chassis with hybrid slots can accommodate older 32-bit
parallel style PXI modules only if the PXI module has a hybrid
compatible connector style. And when using an embedded controller in a PXIe chassis the controller must also be a PXIe form
factor. Instrument drivers from different instrument suppliers are
generally autonomous, and co-exist in the same system without
issue. This application note has been a review of characteristics
to consider when using multi-vendor PXI bases solutions.
Keysight is a sponsor member of the PXI Systems Alliance and
closely works with other PXI SA members to ensure our customers are successful when deploying multi-vendor PXI solutions.
Related information
Software information
Chassis slot compatibility: PXIe system slot
Microsoft Windows XP
Related information
– To find out more about the Keysight PXI products or to attend one of our on-demand or live web events visit us.
– Keysight IO Libraries,
– Keysight IVI Drivers,
– Keysight Chassis,
– Tested Computer List, Keysight publication number
Änderungen und Irrtümer vorbehalten. dataTec 31-07-2015 | © Keysight Technologies 2015, June 15, 2015 | 5991-0384EN
Tips to improve interoperability
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