Getting ready for the retrochallenge. Below is the test circuit I put together, to just check that the CPU is working. 20MHz clock driving the TMS99105, and the TMS99105 is outputting 5MHz CLKOUT signal. The other oscilloscope channel is looking at #MEM signal, which is going nicely low as the processor is fetching data. No memories are connected, the CPU is just running wild, but it seems to be doing something - working!