Honored Contributor
Honored ContributorI have to suspect your power supplies. There's nothing particularly obvious that's wrong with the part of the schematic you've posted.
Does the toggling on nSTATUS look at all like the toggling you've captured on TDO? If TDO was behaving properly it should be responding at the same rate as the TCK or TDI signal you're driving in. Your scope trace shows 1ms per division. That is far too slow for any sensible behaviour. It's more likely to be directly linked to behaviour you have on an FPGA supply rail. Probe around your power supplies, look for any that are dropping out at any point or, more likely, repetitively. That might explain the behaviour you have on TDO and nSTATUS. I note that you've captured your 'EPCS' to accept either SO16 or SO8 parts. This clearly requires additional, unwanted tracking, but I can't see that coming into play here. Regards, Alex
