[SI-LIST] JTAG Guru's


I am hoping there are a few people in the group that
know JTAG fairly well.  I am currently using it now
for flashing in a new design, but I have some
unanswered questions.

The JTAG interface is made up of 5 signals:
TMS : Test Mode Select
TCK : Test Clock
TREST_N : Test Reset
TDI :  Test Data IN
TDO :  Test Data OUT

These signals go into the TAP (Test Access Port) and
allow me to do boundary scan and somehow give the part
test instructions.

Questions:
1.  What happens if I continuously toggle the JTAG
pins when I am not flashing the part (eg, when it is
in 'normal' operation).  Will this cause the processor
to freak out?  Will it matter for some pins but not
others?

2.  I am unsure what the TMS pin does.  Do I need to
continuously do something to this pin..or, do I just
hold it low for testing?  I've read the the TAP
controller responds to "changing" of the TMS and TCK.

3.  After power-up, before I do testing or flashing,
do I need to hold the TRESET_N pin low.

4.  Anyone have a short tutorial for JTAG?

Thanks for your help,

-Trey


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