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Texas Instruments Cascading Multiple Linking Addressable Scan Port Devices Application notes
Application Report
SCTA056 - November 2002
Cascading Multiple-Linking
Addressable-Scan-Port Devices
Rakesh N. Joshi and Kenneth L. Williams
MPD Digital Products
ABSTRACT
This application report is intended to illustrate the capability of cascading multiple Texas
Instruments (TI) linking addressable scan port (LASP)† devices. It explains configuring the
secondary test access ports (TAPs) of cascaded LASPs with the help of a single linking
shadow protocol and protocol-bypass inputs. Several examples of linking shadow protocol,
along with timing requirements and scan data path, are provided. Additionally, it also
discusses linking shadow-protocol errors and the LASP response to these protocol errors.
Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Linking Shadow Protocol and Cascade Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Primary-to-Secondary TAPs Connections and Scan Data Path . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4
Linking Shadow Protocol Errors in Command Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
List of Figures
1
2
3
4
5
6
7
8
An Example of Select-and-Acknowledge Protocol for Addressing and Connecting
Primary-to-Secondary Taps of Three Cascaded LASPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Cascade Connections for Three LASPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Primary-to-Secondary TAPs Connections and Scan Data Path of Three Cascaded LASPs
Using Linking Shadow Protocol or Protocol-Bypass Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Scan Data Path When Position and Configuration for the First LASP
Are Not Received or, if Received, the Configuration Bits are Decoded as 111 . . . . . . . . . . . . . . . . . 7
Scan Data Path When Position and Configuration for the Second LASP
Are Not Received or, if Received, the Configuration Bits are Decoded as 111 . . . . . . . . . . . . . . . . . 8
Scan Data Path When Position and Configuration for the Third LASP
Are Not Received or, if Received, the Configuration Bits are Decoded as 111 . . . . . . . . . . . . . . . . . 9
Scan Data Path When Position and Configuration for the Second and Third LASP
Are Not Received or, if Received, the Configuration Bits are Decoded as 111 . . . . . . . . . . . . . . . . 10
Scan Data Path When Position and Configuration for the First and Third LASP
Are Not Received or, if Received, the Configuration Bits are Decoded as 111 . . . . . . . . . . . . . . . . 11
† For detailed operation of LASP, please refer to the SN74LVT8986 (SCBS759) data sheet.
1
SCTA056
9
10
Scan Data Path When Position and Configuration for the First and Second LASP
Are Not Received or, if Received, the Configuration Bits are Decoded as 111 . . . . . . . . . . . . . . . . 12
Linking Shadow Protocol and Data-Flow Timing for Three Cascaded LASPs . . . . . . . . . . . . . . . . . 15
List of Tables
1
2
2
Secondary TAP Connections and Scan Data Path When Using Linking Shadow Protocol . . . . . . 13
Secondary TAP Connections and Scan Data Path When Using Protocol-Bypass Inputs . . . . . . . 14
Cascading Multiple-Linking Addressable-Scan-Port Devices
SCTA056
1
Introduction
The IEEE 1149.1 standard (JTAG) provides boundary-scan architecture and a serial test bus for
integrated circuits (ICs). Multiple ICs can be connected together on the test bus to allow
accessing all ICs together during board-level testing. Boards equipped with these JTAG ICs can
be connected at the backplane level using two fundamental access schemes. The first scheme
is to serially daisy-chain boards together to allow all boards to be accessed simultaneously. The
second scheme is to provide each board with an addressable interface, such that boards can be
accessed individually. The first scheme suffers from the fact that if one board is removed from
the backplane, access to other boards is disabled. The second scheme overcomes this problem
by using an addressable scheme to access remaining boards in the backplane.
Some boards are designed preferably by partitioning subsets of ICs onto individual scan paths.
This partitioning allows accessing subset groups of ICs separately, which offers several
advantages. One advantage is that ICs that are capable of being accessed at higher JTAG
test-bus clock rates can be included in one group, while ICs that operate at slower test-bus clock
rates can be placed in another group. Thus, test-bus speed binning is possible. Similarly,
complex programmable logic devices (CPLD) and flash memories also could be placed in
subset groups for in-circuit programming. As densities of CPLDs and flash memories increase
and package sizes decrease, it becomes difficult to program them out-of-circuit. Programming
in-circuit is desirable in both development and production environments. For development,
engineers can change the configuration information stored in the CPLD or the code stored in
flash memory devices during the development process. For production, in-circuit programming
allows CPLDs and flash devices to remain on the shelf in an unprogrammed or blank state.
These blank devices then can be installed at assembly and programmed in-circuit, thus reducing
programming and tracking costs.
Another advantage in partitioning ICs onto separate scan paths is that it allows accessing a
first-scan-path group to initiate a self-test operation, then, while that group operates the self-test,
it allows accessing another scan-path group to start testing of another IC group. Still another
advantage is that some ICs may include emulation and debug features that are accessible by
the JTAG test bus. Being able to place these types of ICs in a group separate from other ICs
leads to improvements in execution efficiency of JTAG-based debug and emulation operations.
The LASP uses a linking shadow protocol that is transmitted transparently over the JTAG test
bus. At the backplane level, the linking shadow protocol is used to send an address and
command over the backplane test bus to enable one of a plurality of board-resident LASPs.
Once enabled, the LASP of the addressed board allows the backplane JTAG test bus to
communicate to the ICs of the addressed board. The three secondary TAPs of LASP allow
accessing ICs in the previously mentioned grouping style if the board has a maximum of three
separate scan paths. Thus, a board with more than three separate scan paths would require
multiple LASPs. The capability of cascading a maximum of eight LASPs allows accessing 24
separate scan paths, either individually, in selected combinations, or all linked together into one
scan path.
Cascading Multiple-Linking Addressable-Scan-Port Devices
3
SCTA056
2
Linking Shadow Protocol and Cascade Connections
Figure 1 is an example of a complete select-and-acknowledge protocol for addressing and
connecting primary-to-secondary TAPs of three cascaded LASPs. Each protocol consists of an
address and command fields. Command fields consist of position field and configuration field for
each LASP in the cascade chain. Select-bit pairs frame address and command fields at the
beginning and end, and idle-bit pairs frame the message at the beginning and end. All the
LASPs that are cascaded have the same address applied to the address input pins A9–A0.
Select Protocol (Three LASPs Cascaded)
Message
Position
MSB
LSB
Configuration
LSB MSB LSB
Position
MSB LSB
Configuration
MSB LSB
Position
MSB LSB
Configuration
MSB LSB
MSB
Received at
PTDI
T
I
S
DDDDDDDDDD
S
DDD
DDD
DDD
Address
DDD
DDD
DDD
S
I
T
S
I
T
Command
Acknowledge Protocol (Three LASPs Cascaded)
Message
Position
LSB
Configuration
LSB MSB LSB
MSB
Position
MSB LSB
Configuration
MSB LSB
Position
MSB LSB
Configuration
MSB LSB
MSB
Transmitted at
PTDO
T
I
S
DDDDDDDDDD
S
DDD
DDD
Address
I
S
D(1)
D(0)
HH
LL
LH
HL
DDD
DDD
DDD
DDD
Command
Figure 1. An Example of Select-and-Acknowledge Protocol for Addressing
and Connecting Primary-to-Secondary Taps of Three Cascaded LASPs
Three LASPs are shown cascaded in Figure 2. Each LASP is wired at its primary TAP to
common (multidrop) TAP signals (sourced from a central IEEE Std 1149.1 bus master) and fans
out its secondary to the specific group of IEEE Std 1149.1-compliant devices with which it is
associated. CTDI input of the LASP is wired to the CTDO output of the previous LASP in a
cascade chain. CTDI input of the first LASP in the cascaded chain is not wired and is pulled to
high with an internal pullup. CTDO output of the last LASP in the cascaded chain is not wired.
The position inputs P2–P0 of the first LASP in the cascaded chain are set low. The second LASP
in the cascade chain has its position inputs (P2 and P1) set low, while P0 set high. The third
LASP, which is also the last LASP in the cascaded chain, has its position inputs (P2 and P0) set
low, while P1 is set high. All the LASPs receive the select protocol at its PTDI input; however,
only the last LASP in the cascaded chain transmits the acknowledge protocol at its PTDO
output. During acknowledge protocol and after primary-to-secondary TAPs connections are
established, the remaining LASPs in the cascaded chain have their PTDO outputs in the
high-impedance state (3-state) to avoid bus contention.
4
Cascading Multiple-Linking Addressable-Scan-Port Devices
SCTA056
STMS2
STDI2
STRST2
STDO2
PTDO
PTRST
CTDO
PTMS
PTDI
PTCK
BYP5–BYP0
010
STCK2
STMS1
STDI1
STRST1
STCK1
IEEE Std
1149.1
Compliant
Device
Chain
LASP
P2–P0
CTDI
STDO1
STDI0
IEEE Std
1149.1
Compliant
Device
Chain
STRST0
STCK0
STDO0
STDI2
STRST2
STCK2
IEEE Std
1149.1
Compliant
Device
Chain
A9–A0
PTDO
PTRST
CTDO
PTMS
PTDI
PTCK
BYP5–BYP0
001
STMS2
STDO2
STDI1
STRST1
STCK1
IEEE Std
1149.1
Compliant
Device
Chain
LASP
P2–P0
CTDI
STMS1
IEEE Std
1149.1
Compliant
Device
Chain
STDO1
STDI0
STRST0
STCK0
STDO0
STMS0
IEEE Std
1149.1
Compliant
Device
Chain
A9–A0
STDI2
STRST2
STMS2
STDO2
PTRST
PTDO
CTDO
PTMS
PTDI
PTCK
BYP5–BYP0
000
STCK2
STDI1
STRST1
STMS1
STDO1
IEEE Std
1149.1
Compliant
Device
Chain
LASP
P2–P0
A9–A0
CTDI
STCK1
IEEE Std
1149.1
Compliant
Device
Chain
STRST0
STMS0
STDI0
STCK0
STDO0
IEEE Std
1149.1
Compliant
Device
Chain
TDO
IEEE
TCK
Std
TMS
1149.1
Bus
Master
To
Other
Modules
TDI
TRST
Figure 2. Cascade Connections for Three LASPs
Cascading Multiple-Linking Addressable-Scan-Port Devices
5
SCTA056
3
Primary-to-Secondary TAPs Connections and Scan Data Path
Figure 3 illustrates primary-to-secondary TAPs connections and scan data path of three
cascaded LASPs using linking shadow protocol or protocol-bypass inputs. The first LASP in the
cascaded chain has only STAP0 active, the second LASP has STAP0 and STAP2 active, while
the third or last LASP has all of the three secondary TAPs (STAP0, STAP1, STAP2) active.
Figure 3 also includes the linking shadow protocol and states of protocol bypass inputs required
for the previously mentioned primary-to-secondary TAPs connections. If using protocol bypass
inputs, they should be used for all cascaded LASPs. No mixing of linking shadow protocol and
protocol-bypass inputs should be attempted.
LINKING SHADOW PROTOCOL
Address
LSB
T
I
S
Position
LSB
MSB
S
DDDDDDDDDDD
HL
Configuration
MSB
HL
HL
LSB
Position
LSB
MSB
HL
LH
LH
LH
Configuration
LSB
MSB
HL
HL
HL
Position
LSB
MSB
LH
HL
HL
LH
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
Configuration
MSB
HL
LSB
HL
MSB
HL
HL
S
I
T
CONFIGURATION
PROTOCOL
BIT PAIRS
2
1
0
2
1
0
2
1
0
LH
LH
HL
HL
LH
HL
HL
HL
HL
PROTOCOL BYPASS
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
0
1
1
1
0
0
1
1
0
1
0
0
1
0
0
0
0
STDI2
STDO2
STDI1
CTDO
LASP 2
PTDO
PTDI
PTDI
PTDO
Device
Chain
CTDI
LASP 1
PTDI
Device
Chain
STDO1
STDO0
CTDO
STDI0
Device
Chain
STDI2
Device
Chain
STDO2
Device
Chain
STDI1
CTDI
STDO1
CTDO
LASP 0
STDI0
STDO0
Device
Chain
STDI2
CTDI
Device
Chain
STDO2
STDI1
Device
Chain
STDO1
STDI0
BYP
3
DeviceO
Chain
STDO0
BYP
4
PTDO
BYP
5
Figure 3. Primary-to-Secondary TAPs Connections and Scan Data Path
of Three Cascaded LASPs Using Linking Shadow Protocol or Protocol-Bypass Inputs
6
Cascading Multiple-Linking Addressable-Scan-Port Devices
SCTA056
Primary-to-secondary TAPs connections and scan data path of three cascaded LASPs using
linking shadow protocol or protocol-bypass inputs is shown in Figures 4, 5, and 6. Here, during
the select protocol, position and configuration for one LASP in the cascaded chain are not
received or, if received, the configuration bits are decoded as 111. This allows bypassing a
complete set of device chains from the scan path.
In Figure 4, the first LASP in the cascaded chain has all the three secondary TAPs inactive
because it does not receive its matching position and corresponding configuration or, if received,
the configuration bits are decoded as 111. The second LASP now behaves as the first LASP in
the cascaded chain and has STAP0 and STAP2 active. The third LASP has all three secondary
TAPs (STAP0, STAP1, STAP2) active. When protocol-bypass inputs are used, BYP4 and BYP3 of
the first LASP are set high, the second LASP has BYP4 input set low and BYP3 input set high, so
that it behaves as the first LASP in the cascaded chain.
LINKING SHADOW PROTOCOL
Address
T
I
S
(LASP 0)
S
DDDDDDDDDDD
HL
HL
HL
Address
T
I
S
LH
(LASP 1)
LH
LH
LH
HL
HL
(LASP 1)
S
DDDDDDDDDDD
LH
HL
HL
HL
(LASP 2)
HL
LH
HL
HL
HL
HL
S
LH
HL
HL
HL
HL
S
I
T
(LASP 2)
LH
HL
HL
LH
HL
HL
I
T
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
2
1
I
2
1
0
2
1
0
LH
LH
LH
HL
LH
HL
HL
HL
HL
PROTOCOL BYPASS
5
4
3
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
1
1
1
1
1
0
0
1
0
1
0
0
1
0
0
0
0
STD02
STDI1
STDO1
STDI0
STDO0
Device
Chain
CTDI
LASP 2
PTDO
PTD1
PTDO
PTDI
PTDO
Device
Chain
CTDO
LASP 1
PTDI
LASP 0
Device
Chain
STDI2
Device
Chain
STD02
STDI1
STDO1
STDI0
STDO0
Device
Chain
CTDO
CTDO
CTDI
Device
Chain
CTDI
STDI2
Device
Chain
STD02
STDI1
Device
Chain
STDO1
STDI0
Device
Chain
STDO0
BYP
STDI2
BYP
BYP
Figure 4. Scan Data Path When Position and Configuration for the First LASP Are Not Received
or, if Received, the Configuration Bits are Decoded as 111
Cascading Multiple-Linking Addressable-Scan-Port Devices
7
SCTA056
In Figure 5, the second LASP in the cascaded chain has all three secondary TAPs inactive
because it does not receive its matching position and corresponding configuration or, if received,
the configuration bits are decoded as 111. The first LASP in the cascaded chain has only STAP0
active. The second LASP has all three secondary TAPs inactive, but CTDI input is connected to
CTDO output to pass the scan data between the first and third LASP. The third LASP has all
three secondary TAPs (STAP0, STAP1, STAP2) active.
LINKING SHADOW PROTOCOL
Address
(LASP 1)
(LASP 0)
T
I
S
DDDDDDDDDDD
T
I
S
DDDDDDDDDDD
S
HL
HL
HL
S
HL
HL
HL
HL
LH
LH
LH
HL
HL
LH
LH
HL
LH
HL
(LASP 0)
Address
HL
LH
(LASP 2)
LH
LH
HL
HL
HL
S
LH
HL
HL
HL
HL
S
I
T
(LASP 2)
CONFIGURATION
PROTOCOL
BIT PAIRS
HL
I
T
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
2
1
0
2
1
0
2
1
0
LH
LH
HL
LH
LH
LH
HL
HL
HL
PROTOCOL BYPASS
4
3
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
0
1
1
1
0
0
1
1
1
1
1
0
1
0
0
0
0
CTDI
CTDO
STDI2
STD02
STDI1
STDO1
Device
Chain
CTDO
LASP 2
PTDO
PTDI
PTDI
PTDO
Device
Chain
CTDI
LASP 1
PTDI
STDI0
STDO0
CTDO
CTDI
LASP 0
Device
Chain
STDI2
Device
Chain
STD02
STDI1
Device
Chain
STDO1
STDI0
Device
Chain
STDO0
STDI2
Device
Chain
STD02
STDI1
Device
Chain
STDO1
STDI0
BYP
5
Device
Chain
STDO0
BYP
PTDO
BYP
Figure 5. Scan Data Path When Position and Configuration for the Second LASP
Are Not Received or, if Received, the Configuration Bits Are Decoded as 111
8
Cascading Multiple-Linking Addressable-Scan-Port Devices
SCTA056
In Figure 6, the third LASP in the cascaded chain has all three secondary TAPs inactive
because it does not receive its matching position and corresponding configuration or, if received,
the configuration bits are decoded as 111. The first LASP in the cascaded chain has only STAP0
active. The second LASP has STAP0 and STAP2 active and now behaves as the last LASP in
the cascaded chain. When protocol-bypass inputs are used, the second LASP has BYP4 input
set high and BYP3 input set low, so that it behaves as the last LASP in the cascaded chain. The
BYP4 and BYP3 inputs of the third LASP are set high.
LINKING SHADOW PROTOCOL
Address
(LASP 1)
(LASP 0)
T
I
S
DDDDDDDDDDD
T
I
S
DDDDDDDDDDD
S
HL
HL
HL
S
HL
HL
HL
HL
LH
LH
LH
HL
HL
LH
LH
LH
HL
HL
(LASP 0)
Address
HL
HL
(LASP 2)
LH
HL
HL
LH
HL
S
LH
HL
LH
LH
LH
S
I
T
(LASP 1)
CONFIGURATION
PROTOCOL
BIT PAIRS
HL
I
T
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
2
1
0
2
1
0
2
1
0
LH
LH
HL
HL
LH
HL
LH
LH
LH
PROTOCOL BYPASS
4
3
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
0
1
1
1
0
0
1
0
0
1
0
0
1
1
1
1
1
CTDO
STD02
STDI1
STDO1
Device
Chain
CTDO
LASP 2
PTDO
PTDI
PTDI
PTDO
Device
Chain
CTDI
LASP 1
PTDI
STDI0
STDO0
CTDO
CTDI
LASP 0
Device
Chain
STDI2
Device
Chain
STD02
STDI1
STDO1
STDI0
Device
Chain
PTDO
CTDI
Device
Chain
STDO0
STDI2
Device
Chain
STD02
STDI1
Device
Chain
STDO1
STDI0
BYP
5
Device
Chain
STDO0
BYP
STDI2
BYP
Figure 6. Scan Data Path When Position and Configuration for the Third LASP
Are Not Received or, if Received, the Configuration Bits Are Decoded as 111
Cascading Multiple-Linking Addressable-Scan-Port Devices
9
SCTA056
Primary-to-secondary TAPs connections and the scan data path of three cascaded LASPs using
linking shadow protocol or protocol-bypass inputs is shown in Figures 7, 8, and 9. Here, during
the select protocol, position and configuration for only one LASP in the cascaded chain is
received or, if received for more than one, the configuration bits are decoded as 111, except for
one. This allows operating the device as a single device and bypassing the rest of the devices in
cascaded chains from the scan path.
In Figure 7, during the select protocol, position and configuration for the second and third LASP
are not received or, if received, their configuration bits are decoded as 111. The first LASP in the
cascaded chain has only STAP0 active and now behaves as a single LASP (not cascaded). The
second and third LASP have all three secondary TAPs inactive. When protocol-bypass inputs
are used, the first LASP has its BYP4 and BYP3 inputs set low, so that it behaves as a single
LASP (not cascaded). The BYP4 and BYP3 inputs of the second and third LASPs are set high.
LINKING SHADOW PROTOCOL
Address
(LASP 1)
(LASP 0)
T
I
S
DDDDDDDDDDD
T
I
S
DDDDDDDDDDD
S
HL
HL
HL
S
HL
HL
HL
HL
LH
LH
LH
LH
LH
S
HL
HL
LH
(LASP 2)
LH
LH
HL
LH
HL
LH
LH
LH
S
I
T
(LASP 0)
Address
HL
CONFIGURATION
PROTOCOL
BIT PAIRS
I
T
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
2
1
0
2
1
0
2
1
0
LH
LH
HL
LH
LH
LH
LH
LH
LH
PROTOCOL BYPASS
4
3
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
0
0
1
1
0
0
1
1
1
1
1
0
1
1
1
1
1
CTDO
STDI2
Device
Chain
STDO2
STDI1
STDO1
Device
Chain
CTDI
LASP 1
CTDO
LASP 2
PTDO
PTDI
PTDO
STDI0
STDO0
STDI2
CTDI
LASP 0
Device
Chain
Device
Chain
STDO2
STDI1
STD01
STDI0
Device
Chain
PTDI
CTDO
Device
Chain
STDO0
STDI2
Device
Chain
STDO2
STDI1
STDO1
STDI0
Device
Chain
CTDI
PTDI
BYP
5
Device
Chain
STDO0
BYP
PTDO
BYP
Figure 7. Scan Data Path When Position and Configuration for the Second and Third LASPs
Are Not Received or, if Received, the Configuration Bits Are Decoded as 111
10
Cascading Multiple-Linking Addressable-Scan-Port Devices
SCTA056
In Figure 8, during the select protocol, position and configuration for the first and third LASPs are
not received or, if received, their configuration bits are decoded as 111. The second LASP in the
cascaded chain has STAP0 and STAP2 active and now behaves as a single device (not
cascaded). The first and third LASPs have all the three secondary TAPs inactive. When
protocol-bypass inputs are used, the second LASP has its BYP4 and BYP3 inputs set low, so
that it behaves as a single LASP (not cascaded). The BYP4 and BYP3 inputs of first and third
LASPs are set high.
Address
LINKING SHADOW PROTOCOL
(LASP 1)
(LASP 0)
T
I
S
DDDDDDDDDDD
T
I
S
DDDDDDDDDDD
S
HL
HL
HL
S
LH
HL
HL
LH
LH
LH
LH
LH
HL
S
HL
HL
HL
LH
HL
(LASP 2)
HL
LH
HL
LH
LH
LH
S
I
T
(LASP 1)
Address
HL
CONFIGURATION
PROTOCOL
BIT PAIRS
I
T
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
2
1
0
2
1
0
2
1
0
LH
LH
LH
HL
LH
HL
LH
LH
LH
PROTOCOL BYPASS
BYP
5
4
3
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
1
1
1
1
1
0
0
0
0
1
0
0
1
1
1
1
1
CTDO
STDI2
STDO2
STDI1
STDO1
Device
Chain
CTDO
LASP 2
PTDI
PTDI
PTDO
Device
Chain
CTDI
LASP 1
PTDI
STDI0
STDI2
CTDI
LASP 0
Device
Chain
STDO0
Device
Chain
STDO2
STDI1
Device
Chain
STD01
STDI0
STDO0
STDI2
CTDO
Device
Chain
PTDO
CTDI
Device
Chain
STDO2
STDI1
Device
Chain
STDO1
STDI0
Device
Chain
STDO0
BYP
PTDO
BYP
Figure 8. Scan Data Path When Position and Configuration for the First and Third LASPs
Are Not Received or, if Received, the Configuration Bits Are Decoded as 111
Cascading Multiple-Linking Addressable-Scan-Port Devices
11
SCTA056
In Figure 9, during the select protocol, position and configuration for the first and second LASPs
are not received or, if received, their configuration bits are decoded as 111. The third LASP in
the cascaded chain has all three secondary TAPs active and now behaves as a single device
(not cascaded). The first and second LASPs have all three secondary TAPs inactive. When
protocol-bypass inputs are used, the third LASP has its BYP4 and BYP3 inputs set low, so that it
behaves as a single LASP (not cascaded). The BYP4 and BYP3 inputs of the first and second
LASPs are set high.
LINKING SHADOW PROTOCOL
Address
(LASP 1)
(LASP 0)
T
I
S
DDDDDDDDDDD
T
I
S
DDDDDDDDDDD
S
HL
HL
HL
S
HL
LH
HL
LH
LH
LH
LH
HL
HL
S
HL
HL
LH
(LASP 2)
LH
LH
HL
LH
HL
HL
HL
HL
S
I
T
(LASP 2)
Address
HL
CONFIGURATION
PROTOCOL
BIT PAIRS
I
T
CONFIGURATION
PROTOCOL
BIT PAIRS
CONFIGURATION
PROTOCOL
BIT PAIRS
2
1
0
2
1
0
2
1
0
LH
LH
LH
LH
LH
LH
HL
HL
HL
PROTOCOL BYPASS
BYP
5
4
3
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
0
1
1
1
1
1
0
1
1
1
1
1
0
0
0
0
0
0
CTDI
STDI2
Device
Chain
STDO2
STDI1
STDO1
Device
Chain
CTDI
CTDO
PTDI
LASP 2
PTDI
PTDO
STDI0
STDO0
CTDO
LASP 1
PTDI
LASP 0
Device
Chain
STDI2
Device
Chain
STDO2
STDI1
Device
Chain
STDO1
STDI0
STDO0
STDI2
CTDO
Device
Chain
PTDO
CTDI
Device
Chain
STDO2
STDO1
STDI0
STDI1
Device
Chain
Device
Chain
STDO0
BYP
PTDO
BYP
Figure 9. Scan Data Path When Position and Configuration for the First and Second LASPs
Are Not Received or, if Received, the Configuration Bits Are Decoded as 111
12
Cascading Multiple-Linking Addressable-Scan-Port Devices
SCTA056
Secondary TAP connections and scan data path, when using linking shadow protocol or
protocol-bypass inputs, are shown in Tables 1 and 2. Secondary TAP connections and scan data
path are shown when the position of the LASP within the cascade chain is first, last, not first nor
last, and when it is used as a single device.
Table 1. Secondary TAP Connections and Scan Data Path
When Using Linking Shadow Protocol
Configuration
Position
Single device
First device in cascade
chain
Last device in cascade
chain
Not first/last device in
cascade chain
STAP Configuration
BIT 2
BIT 1
BIT 0
1
1
1
Scan Data Path
STAP2
STAP1
STAP0
1
Inactive
Inactive
Inactive
None
1
0
Inactive
Inactive
Active
PTDI – STAP0 – PTDO
1
0
1
Inactive
Active
Inactive
PTDI – STAP1 – PTDO
1
0
0
Inactive
Active
Active
PTDI – STAP0 – STAP1 – PTDO
0
1
1
Active
Inactive
Inactive
PTDI – STAP2 – PTDO
0
1
0
Active
Inactive
Active
PTDI – STAP0 – STAP2 – PTDO
0
0
1
Active
Active
Inactive
PTDI – STAP1 – STAP2 – PTDO
0
0
0
Active
Active
Active
PTDI – STAP0 – STAP1 – STAP2 – PTDO
1
1
1
Inactive
Inactive
Inactive
None
1
1
0
Inactive
Inactive
Active
PTDI – STAP0 – CTDO
1
0
1
Inactive
Active
Inactive
PTDI – STAP1 – CTDO
1
0
0
Inactive
Active
Active
PTDI – STAP0 – STAP1 – CTDO
0
1
1
Active
Inactive
Inactive
PTDI – STAP2 – CTDO
0
1
0
Active
Inactive
Active
PTDI – STAP0 – STAP2 – CTDO
0
0
1
Active
Active
Inactive
PTDI – STAP1 – STAP2 – CTDO
0
0
0
Active
Active
Active
PTDI – STAP0 – STAP1 – STAP2 – CTDO
1
1
1
Inactive
Inactive
Inactive
None
1
1
0
Inactive
Inactive
Active
CTDI – STAP0 – PTDO
1
0
1
Inactive
Active
Inactive
CTDI – STAP1 – PTDO
1
0
0
Inactive
Active
Active
CTDI – STAP0 – STAP1 – PTDO
0
1
1
Active
Inactive
Inactive
CTDI – STAP2 – PTDO
0
1
0
Active
Inactive
Active
CTDI – STAP0 – STAP2– PTDO
0
0
1
Active
Active
Inactive
CTDI – STAP1 – STAP2 – PTDO
0
0
0
Active
Active
Active
CTDI – STAP0 – STAP1 –STAP2 – PTDO
1
1
1
Inactive
Inactive
Inactive
CTDI – CTDO
1
1
0
Inactive
Inactive
Active
CTDI – STAP0 – CTDO
1
0
1
Inactive
Active
Inactive
CTDI – STAP1 – CTDO
1
0
0
Inactive
Active
Active
CTDI – STAP0 – STAP1 – CTDO
0
1
1
Active
Inactive
Inactive
CTDI – STAP2 – CTDO
0
1
0
Active
Inactive
Active
CTDI – STAP0 – STAP2– CTDO
0
0
1
Active
Active
Inactive
CTDI – STAP1 – STAP2 – CTDO
0
0
0
Active
Active
Active
CTDI – STAP0 – STAP1 –STAP2 – CTDO
Cascading Multiple-Linking Addressable-Scan-Port Devices
13
SCTA056
Table 2. Secondary TAP Connections and Scan Data Path
When Using Protocol-Bypass Inputs
STAP Configuration
BYP
14
Scan Data Path
5
4
3
2
1
0
STAP2
STAP1
STAP0
0
0
0
1
1
1
Inactive
Inactive
Inactive
None
0
0
0
1
1
0
Inactive
Inactive
Active
PTDI – STAP0 – PTDO
0
0
0
1
0
1
Inactive
Active
Inactive
PTDI – STAP1 – PTDO
0
0
0
1
0
0
Inactive
Active
Active
PTDI – STAP0 – STAP1 – PTDO
0
0
0
0
1
1
Active
Inactive
Inactive
PTDI – STAP2 – PTDO
0
0
0
0
1
0
Active
Inactive
Active
PTDI – STAP0 – STAP2 – PTDO
0
0
0
0
0
1
Active
Active
Inactive
PTDI – STAP1 – STAP2 – PTDO
0
0
0
0
0
0
Active
Active
Active
PTDI – STAP0 – STAP1 – STAP2 – PTDO
0
0
1
1
1
1
Inactive
Inactive
Inactive
None
0
0
1
1
1
0
Inactive
Inactive
Active
PTDI – STAP0 – CTDO
0
0
1
1
0
1
Inactive
Active
Inactive
PTDI – STAP1 – CTDO
0
0
1
1
0
0
Inactive
Active
Active
PTDI – STAP0 – STAP1 – CTDO
0
0
1
0
1
1
Active
Inactive
Inactive
PTDI – STAP2 – CTDO
0
0
1
0
1
0
Active
Inactive
Active
PTDI – STAP0 – STAP2 – CTDO
0
0
1
0
0
1
Active
Active
Inactive
PTDI – STAP1 – STAP2 – CTDO
0
0
1
0
0
0
Active
Active
Active
PTDI – STAP0 – STAP1 – STAP2 – CTDO
0
1
0
1
1
1
Inactive
Inactive
Inactive
None
0
1
0
1
1
0
Inactive
Inactive
Active
CTDI – STAP0 – PTDO
0
1
0
1
0
1
Inactive
Active
Inactive
CTDI – STAP1 – PTDO
0
1
0
1
0
0
Inactive
Active
Active
CTDI – STAP0 – STAP1 – PTDO
0
1
0
0
1
1
Active
Inactive
Inactive
CTDI – STAP2 – PTDO
0
1
0
0
1
0
Active
Inactive
Active
CTDI – STAP0 – STAP2– PTDO
0
1
0
0
0
1
Active
Active
Inactive
CTDI – STAP1 – STAP2 – PTDO
0
1
0
0
0
0
Active
Active
Active
CTDI – STAP0 – STAP1 –STAP2 – PTDO
0
1
1
1
1
1
Inactive
Inactive
Inactive
CTDI – CTDO
0
1
1
1
1
0
Inactive
Inactive
Active
CTDI – STAP0 – CTDO
0
1
1
1
0
1
Inactive
Active
Inactive
CTDI – STAP1 – CTDO
0
1
1
1
0
0
Inactive
Active
Active
CTDI – STAP0 – STAP1 – CTDO
0
1
1
0
1
1
Active
Inactive
Inactive
CTDI – STAP2 – CTDO
0
1
1
0
1
0
Active
Inactive
Active
CTDI – STAP0 – STAP2– CTDO
0
1
1
0
0
1
Active
Active
Inactive
CTDI – STAP1 – STAP2 – CTDO
0
1
1
0
0
0
Active
Active
Active
CTDI – STAP0 – STAP1 –STAP2 – CTDO
1
X
X
X
X
X
As requested by linking shadow protocol
Cascading Multiple-Linking Addressable-Scan-Port Devices
SCTA056
Linking shadow protocol and data-flow timing for three cascaded LASPs is shown in Figure 10.
The linking shadow protocol result is a match and the prior connect status is OFF. The first
LASP (LASP0) in the cascade chain has only STAP0 active, the second LASP (LASP1) has
STAP0 and STAP2 active, while the third or last LASP (LASP2) has all three secondary TAPs
(STAP0, STAP1, STAP2) active.
PTCK
A9–A0
Don’t Care
Don’t Care
LASP0/P2–P0
Don’t Care
Don’t Care
LASP1/P2–P0
Don’t Care
Don’t Care
LASP2/P2–P0
LASP2–0/BYP5
Don’t Care
Don’t Care
LASP2–0/BYP4–BYP0
PTDI
Dont’ Care
Idle Select
A0p-A9p
Select
Command Select Idle
Don’t Care
Don’t Care
PTMS
PTRST
Don’t Care
LASP2–0/STDI2–STDI0
LASP2/CON2–CON0
111
000
LASP1/CON2–CON0
111
010
LASP0/CON2–CON0
111
110
PTDO
Idle Select
A0p-A9p
Select
Command Select Idle
STDI2 of LASP2
LASP2/CTDO
STDI2 of LASP2
LASP2/STDO2
STDI1 of LASP2
LASP2/STDO1
STDI0 of LASP2
LASP2/STDO0
CTDI of LASP2
LASP1/CTDO
STDI2 of LASP1
LASP1/STDO2
STDI0 of LASP1
LASP1/STDO1
LASP1/STDO0
CTDI of LASP1
LASP0/CTDO
STDI0 of LASP0
LASP0/STDO2
LASP0/STDO1
LASP0/STDO0
PTDI
Figure 10. Linking Shadow Protocol and Data-Flow Timing for Three Cascaded LASPs
Cascading Multiple-Linking Addressable-Scan-Port Devices
15
SCTA056
4
Linking Shadow Protocol Errors in Command Field
The command field received during the select protocol is required to be a multiple of 6-bit pairs,
otherwise the protocol result is HARD ERROR. The receipt of a long command field, i.e., greater
than 48-bit pairs, also results in HARD ERROR. If the configuration field received in the
single-device mode is decoded as 111 or all the configuration fields received when multiple
LASPs are cascaded are decoded as 111, the protocol result is HARD ERROR. When the
protocol result is HARD ERROR, connections to LASPs are dissolved.
If the number of positions and configurations received is greater than actual LASPs cascaded, or
if a received position does not match that of any cascaded LASPs, then the LASP operation is
undefined.
5
Summary
The capability of cascading a maximum of eight LASPs exists. This allows accessing 24
separate scan paths, either individually, in selected combinations, or all linked together into one
scan path. The secondary TAPs of all the cascaded LASPs can be configured using a single
linking shadow protocol or protocol bypass inputs. All cascaded LASPs share the same address;
as such, their A9–A0 inputs are tied together. The position inputs P2–P0 identify their position in
the cascaded chain. The position and corresponding configuration bits received during linking
shadow protocol determine the primary-to-secondary TAPs connections for the matching LASP.
When protocol-bypass inputs are used, inputs BYP4 and BYP3 identify the position of LASP in
the cascaded chain, while inputs BYP2–BYP0 configure the primary-to-secondary TAPs
connections.
6
References
1. A Proposed Method of Accessing 1149.1 in a Backplane Environment (SCTA032).
2. Partitioning Designs With 1149.1 Scan Capabilities (SCTA031).
16
Cascading Multiple-Linking Addressable-Scan-Port Devices
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