Adding an 8085 CPU on a Z80 Bus for the RC2014 computer @_feilipu @ZxSpectROM

feilipu blogs about making an 8085 add-on card for the RC2014 computer. The RC2014 is based on a Zilog Z80 and related peripherals and the timing signals for each microprocessor are rather different.

For the 8085, the Intel architects took the bus interface in another direction. They integrated several components from the support chips for the 8080 into the silicon die, and produced new features which made the 8085 much more useful as a micro-controller than the Z80.  For the bus, the major change was to multiplex the data lines with the low address lines. This step allowed them to reuse the 8 saved lines on the 40-pin DIP for other purposes.

Multiplexing the address and data lines meant that they had to add an external address latch, to capture the lower address values, before either writing data or reading data from the bus. The normal read and write lines are present and they behave in a similar manner to the Z80.

See how Phillip was able to generate Z80 compatible signals from 8085 control lines and make a compatible card and also a version of BASIC for the 8085 in the post here.


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