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Altera_Forum
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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
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14 years ago

Are you sure you don't have an external micro short circuit between TMS and ground, such as a small metal piece or some solder?

It could also be a clamping diode to GND that is failing. This could be caused by an ESD pulse or a negative voltage applied by accident to the pin. Do you have any kind of protection between the FPGA JTAG pins and the connector?