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, "DanielB" <danlb_2000@...> wrote:
> The IMSAI 8080 I recently posted about came with a Dutronics DZ80-80. I couldn't find any information on this board online so I traced out the circuit. If anyone is interested you can get the schematics here:
> I haven't checked it over thoroughly so there may be errors. It's pretty interesting everything that needs to be done to adapt a Z80 to an 8080 system. For example there is a circuit to detect the Z80 DI and EI instructions which disable and enable the makeable interrupt so that the 8080 INTE signal can be simulated. There is also a circuit to handle the difference in what the Z80 and 8080 do with the upper 8 bits of the address bus during IO operations.
> The one question I still have is about the Z80 MREQ signal which is brought out to a wire coming off the board. Not sure what this wire would be used for.
Very cool. I started working on this through pictures sent by Corey, but without the actual board to trace and ohm, it became too much of a guessing game. I managed to map out the remaping of the upper 8 bits of the address bus, and the diode clock circuit for the non-ttl clock from the 8080. I have several examples of Z80 to 8080 circuits, thought I might be able to match things up, but didn't get there yet.
Thanks for doing a very nice job at tracing things out, very cool!
I found a good write up about this board at
Look at page 42.
My guess about the MREQ, is there must have been some custom board that needed a Z80 timing signal.