I had given that some thought (as a way around the multi-port update issue, but not as a simple solution with a serial cable), my only concern is I would like to test it at speed. Serial cable into a shift register, can we just call that a DC test as a close approximation?
If you don't mind slow, that is certainly the low cost way and I have all the parts, so thanks for that idea.
I not only want a quick way to know if all the output patterns are correct, but it would be nice to see how fast this network runs before it craps out and I expect it will run at 10mhz just fine.