Forum Discussion
Altera_Forum
Honored Contributor
13 years agoHi Dave,
I just had the same problem with the TDO pin on the JTAG. I have a cyclone IV chip that has been working just fine. All of a sudden the JTAG stopped working. The TDO was shorted to ground with 40 ohms. It was still working, but just a lower voltage(.5V swing). Following your suggestion I applied 3.8V to the pin and the resistance went up to 200 ohm. Now it works. Like you I would like to know what happened so I can keep it from happening again. The JTAG is configured to work on 2.5V correctly and everything worked just fine up until it didn't. I only have protection diodes on the ASDO etc pins to the EPCS device as Altera suggested. They don't recommend anything if your just going to their programmer. Dan