Answers Database

BOUNDARY SCAN/JTAG: Preventing inadvertent activation of boundary scan in XC4K/XC5K devices


Record #239

Problem Title:
BOUNDARY SCAN/JTAG: Preventing inadvertent activation of boundary scan
in XC4K/XC5K devices



Problem Description:
Keywords: inadvertent, activation, bounday scan, jtag, xc4000,
xc5200, tck, tms, pullup, test logic reset

Urgency: Standard

General Description:

How to prevent inadvertent activation of boundary scan?


Solution 1:

When a XC4K/XC5K device powers up, ideally the TAP controller
is in the Test-Logic-Reset state.

For various reasons, a situation may occur where the TMS and
TCK pins of the TAP may toggle forcing the TAP controller out of
the Test-Logic-Reset state. This will cause the device to go in
to the Boundary Scan mode. If this happens during configuration,
it may disrupt the configuration process.

The TMS and TCK pins of the device must be pulled up high before
powerup to prevent inadvertent activation of boundary scan.




End of Record #239