Nexys A7: Need to probe UART signals at FPGA

[btoschi]

Hello,

I have a Nexys A7 and work for the Mega65 project where I need to check timing of the UART protocol with my oscilloscope.
Unfortunately, the schematics of the Nexys are omitting the USB/UART part ("intentionally left blank"), thus I had to inspect the Board:
Tracing the Ch B lines of FT2232H I see there is another IC in-between, which I failed to identify. Marking is hard to read, but looks like ON LC126, but I don't see a datasheet for it.
Can you advise me where I can best probe RX/TX signals coming from FPGA and also tell me which IC is in-between FPGA and FT2232H ?

Thanks & Best,
  B. Toschi

[artvvb]

Hi @btoschi

Apologies for the delay.

As you've seen, Digilent doesn't provide the USBUART circuitry, as it's part of the JTAG programming solution. The IC between the FPGA and FT2232H is a non-inverting buffer that is only enabled when PGOOD from the power supplies is high.

For some alternate ideas: 1. You could forward the UART signals to other pins, like on a Pmod connector. 2. Instead of an oscilloscope, you could use an ILA wired up to RX and TX inside of the FPGA to get a view of the waveforms.

Thanks,

Arthur