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Does anyone know if it is possible to loopback Altera Byteblaster 10-pin Header JTAG Mode signals in order to accomplish automated self-test, to verify the cable and header connector are good?
I'm thinking just loopback TDO to TDI, and then check to verify the signal that comes back is the same as what was sent? If that works, what can be done to verify TCK and TMS also work ?
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If you are using the Parallel Port ByteBlaster, then you can just toggle the pins. The cable needs to be attached to a board, since the buffer within the cable is powered by the board. Toggle TCK/TMS/TDI directly.
Look at the JTAG TAP machine. If you reset the TAP machine (TMS high and toggle TCK 5 or 6 times), the IDCODE gets loaded into the DR register. Move the TAP machine to the DR state, and shift out the IDCODE. You should see TDO toggling. You can put the TAP machine in BYPASS mode by loading the BYPASS instruction into the IR, and then just toggle TDI through to TDO.
Cheers,
Dave
