One beauty of using the PSoC to emulate peripherals is that it can single-step through IO code. I used that a lot in debugging the SIO emulator. Plus, having a CMOS processor let me stall the processor as the PSoC single stepped. Grabbing the Z80 lines with my DSLogic+ Logic Analyzer makes this easy.

The PSoC in-circuit debugger allow breakpoints to be set and code single stepped.

The logic analyzer can show the static value of lines as well as trigger on levels or edges.