Hi Neil! Thanks! John said exactly what I was going to suggest. Set the jump address to 0000H and remove the EPROM. Possibly “JUMP_ENABLE” high or low depending on its state.
I can see there is a major design consideration we are going to have to address in the S-100 Utility board though. Since the MSX engine it is the “rest of the guts” of an MSX machine minus the Z80 CPU, V9938, and AY-3-8910, its circuitry controls basically everything the Z80 CPU can ever see. It has absolute control in an MSX computer.
MSX engine exclusivity is not true in an S-100 bus environment. There could be all sorts of memory (ROMs) and IO outside the purview of the MSX engine circuitry. We are going to have to make the board work in concert with the rest of the S-100 bus contents.
In fact, there is no assurance on an S-100 bus machine there is even a Z80 CPU present. I suppose it is possible to have an 8088 or 6502 connected to the S-100 Utility board and S-100 VDP board and have a bizarre form of non-Z80 MSX. Wow, that would be weird.
I would like the S-100 Utility board to be generally useful and not specific to MSX. I think it could be a single board solution for ROM/RAM/serial/parallel in addition to a bare CPU board to bring up an S-100 machine with just two boards installed. That would help builders with debugging CPU boards and S-100 systems in general. However it looks like the S-100 Utility board is going to need some adjustments to share the bus.
Thanks and have a nice day!