Posted By
gerliczer
on 2013-07-31
02:53:31
|  Re: Z80 GUI: SymbOS
Hi guys,
You came up with a lot of things about processors, OSes and computers. I try to add my 2 cents to some of the topics as a complete hardware amateur. First, I have to tell that having a Z80 connected to the plus/4 or it running GUI OSes seems to be superfluous to me. As someone's pet project it is OK, but beyond that what for?
The CP/M cartridges for the plus/4 cannot be built as the ones for C=64, because there is no externally available mechanism to disable the CPU in the 264 series machines. It would need hardware modifications which are probably not impossible as there are unused pins in the expansion port and next to the CPU there is an 74 series logic IC identical to the one in the 64 with the necessary two gates available. The problem is the port connector and how the unused pins are handled in the available cartridges. Under unfortunate conditions (e.g. unused pins are grounded) the modded machine may lose compatibility with them. Once I was having a message exchange with BSZ about this topic. He said that there _may_ be another way but as he too is busy with his real life I don't think there will be any developments.
If a Z80 is eventually gets connected to a 65XX based machine it won't necessarily must be run on the system clock. If its clock is derived (multiplied) from the system clock then it should be relatively simple to buffer the memory accesses. The Z80 does not turn to the memory in every clock cycle contrary to the 65XX and in a newly designed expansion its control and wait signals are obviously available. Actual Z80 systems like the CPC and Enterprise utilize this feature in various ways.
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