Problems with JTAG and LH79520

From: db (javaguy11111_at_yahoo.com)
Date: 04/14/04 

Date: 13 Apr 2004 21:51:11 -0700

I am in the process of writing a JTAG controller for an LH79520 board
 I am building.

At this point I have been able to successfully access the instruction
and data registers. To verify that things are working I have run loop
back tests through the registers. The problem I am having is that none
of the instructions in the bsdl are working
.
For example, if I try to run the IDCODE command (1110) I am put into
BYPASS when I try to access the data register. From the JTAG spec,
this means that 1110 is not being considered a valid code. This is in
spite of the fact that I am getting a proper capture result when I
clock my instruction into the instruction register.

After some experimentation I have been able to connect the boundary
scan chain and clock data through it, but the codes that give this
result are completely different from the codes in the bsdl file. In
addition I still have not been able to access the IDCODE register.

I do not think it is a board problem, because I do have some code
written for a JTAG/USB controller from Mesa Electronics that is
successfully pulling the IDCODE.

So at the moment I am totally baffled as to why IDCODE is not
accessible and why none of JTAG instructions are working.

I do have the source code for the controller from Mesa Electronics,
but it is written for the Borland compiler. I have downloaded the free
compiler from Borland and am attempting to get it running so I can
enable the debug and see how it is able to get the IDCODE.

In the mean time I am hoping someone may be able to offer some
suggestions on what might be going on.

Relevant Pages

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