I’ve faked the missing power-on reset generator IC by bringing the RESET! low. Unfortunately for some reason I’ve also had to bring the NMI! low afterwards to get the CPU to start.
Since using Leon’s Test EPROM doesn’t produce the results programmed I’ve booted the CPU without any EPROM in the first address. This make the CPU hunt for an answering address and allows checking the address and data buses.
In any case, with or without an EPROM in the first socket I get no VMA signal. I’ve resocketed the CPU with the VMA Pin 5 unconnected to anything just to make sure the two AND gates aren’t dragging it down.
Still no VMA signal. What would cause the 6808 not to produce it?
Yes, brand new 6808, twice in case of a bad run; RAM doesn’t matter with no program; have the 4Mcps clock; IRQ is pulsing;E is going out; R/W is going out.
Data Sheets and circuit schematics can be found here.