Answers Database

M1.3/M1.4 JTAG Programmer: Possible cause of Boundary Scan Chain Integrity error


Record #2881

Product Family:  Software

Product Line:  EPLD Core

Problem Title:
M1.3/M1.4 JTAG Programmer: Possible cause of Boundary Scan Chain
Integrity error



Problem Description:
Keywords: boundary-scan, chain, integrity, check, test, jtag programmer

Urgency: standard

General Description:

You may get the following error when using the M1.3/M1.4 JTAG Programmer

JTAG Programmer Started 1997/09/29 10:03:29

Loading Boundary-Scan Description Language (BSDL) file 'C:/Xilinx/data/xc9536.bs
d'.....completed successfully. Checking boundary-scan
chain integrity...ERROR:basut - Boundary-scan chain test failed at bit position

'0' on instance 'At17cisp(Device1)'. Check that the cable, system and device
JTAG TAP connections are correct, that the target system power supply is set to

the correct level, that the system grounds are connected and that the parts are

properly decoupled.

ERROR:basut - Boundary scan chain has been improperly specified.  Please check
your configuration and re-enter the boundary-scan chain information.
Boundary-scan chain validated unsuccessfully.


Solution 1:

Chain integrity must be assured before the results of the
Boundary Scan testing can be relied upon. A chain may have many
faults that can interfere with the integrity of the chain, e.g.

A component in the chain may be missing, dead or incorrectly
loaded.

A component in the chain may have a broken connection on one of
its TAP pins.

A TDO to TDI connection between two components could be shorted to
another node.

A component in the chain may not have sufficient power supply.

System or Clock noise could cause a component in the chain to jump
TAP states.

A combination of all the problems described above may exist in a
chain of components making it very difficult to diagnose.

The JTAG Programmer performs the integrity test by relying on the
ICs ability to write a fixed data pattern in its Instruction
Register in the Capture-IR state of the TAP Controller. This
concatenated data can then be shifted out on the TDO pin of last
IC. The value of attribute INSTRUCTION_CAPTURE in the BSDL
(Boundary Scan Description Language) file for each device in the
chain shows what this data will be. Additionally, the IEEE
standard 1149.1 mandates that the two LSBs of this data should be
"01".

For a simple test case, assume that there are three devices in the
chain and the Instruction Registers are only two bit wide. In this
case, for a good chain we will see a data of "010101" coming out
on the TDO pin of the last IC.

As an example of a bad chain assume that there is something wrong
with the connection of the first device in the chain. This device
then will not output a "01" on its TDO pin. Instead, it may push a
value such as "11". We will see a data of "110101" coming out on
the TDO pin of the last device. By examining the data stream
closely, we can see that the last two devices in the chain are
connected properly and there is a problem with the first device in
the chain.

The JTAG programmer will issue a 'Boundary Scan Integrity' error
if receives unexpected data at the TDO pin of the last IC. The
integrity failure can occur for a single device as well as for
multiple devices in the chain.



End of Record #2881