Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
14 years ago

TMS stuck low on CYCLONE III

Yesterday we had been happily programming our cyclone III based prototype via JTAG, Quartus and a USB blaster fine until all of a sudden we could no longer detect the JTAG chain! I traced the ...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
14 years ago

Thanks Daixiwen

Pretty sure it isn't a micro short as I have the same problem on two boards. Also I have checked very carefully, cleaned and re-cleaned .

Your second suggestion is possible though. There is no protection between the JTAG header and the FPGA. A negative voltage could have been applied when the USB Blaster was plugged in to the JTAG header on the board. This could have damaged the clamping diode. The engineer tells me he may have had the JTAG disconnected while he ran some tests then plugged it in to re-program the FPGA! Which then failed to detect the chain!

Thanks

Dave