VaheJ

I confirmed that the GPIO has no level shifting that occurs to output. It is directly the FMC voltage (the FPGA output level 1.8V in my case). The PS2-PMOD resistor pullups would interfere with level shifting so I removed it and directly wired it to the PS2 din connector on the mouse adapter. I used the VC707's 1.8V source on J14 header left pin located right under the Board Power Port. I was originally bringing down the voltage down from 5V using a resistor divider on my PCA9306 level translator, but I removed that once I had established the reference voltage on the low side of the PCA9306. Now the two sides, 1.8V and 5V are from separate sources. Measurement on my oscilloscope confirmed that the level was properly translated to output at 5V and back to input at 1.8V mouse for the FPGA. See the final setup.

Thank you for the updated support answer. I appreciate it. I have one more question if I can ask, but its related to my original question. It's about adding the actual mouse to the FMC-CE as I an externally powered PS2 PMOD connected to the 6 pin gpio on the FMC-CE. It is set to 5V because I was not getting back responses from the mouse at all. The mouse is a USB trackball and under this voltage it inconsistently responds with burst packets when I send commands. Do I need an appropriate bidirectional level shifter at all to properly convert the 3.3V from the GPIO FMC-CE to the 5V pullup on the PS2 PMOD?

Thank You for the information. If they are supposed to be inout (bidirectional) as in the case of a real mouse. How do I preserve the bidirectional flow instead of making one just input or output as opposed to inout. Is this possible still? My two signals are a clock and data which are supposed to be controlled by tristates on each side ( each side is its own system - that I have on my FPGA). If I make one input and one output the inout nature will change.

I have a VC707 FPGA and a FMC-CE GPIO Expansion Card. I want to loop back two GPIO pins to two other GPIO pins respectively to communicate inout signals between two embedded FPGA modules implemented so I can observe module behavior. With out loopback I have a real external peripheral connected. It does not initialize leading me to suspect an issue in the controlling module. So I came up with an idea to emulate the mouse inside the FPGA and using the GPIO card I thought I could send the two respective signals back into the FPGA between the controller module and my created emulation module of the mouse. Is this approach safe? Do I just connect the pins from the header or do I need to use series resistors to safely loopback? Please advise.