Damn! It looks like the Z280 is probably not going to be a good match for the Enterprise ... the CPU itself runs at half the speed of the external clock.

Same problem with the original Z180. But the Z8S180 version have a option for double the the clock, then you got the right speed.

Same problem with the original Z180. But the Z8S180 version have a option for double the the clock, then you got the right speed.

Have you actually tried a Z8S180?

How did your experiment with the Z180 work out?

Did EXOS/EXDOS/IS-DOS/BASIC all work without using any of the undocumented IXH/IXL/IYH/IYL instructions?

I don't think any of the standard EP software uses undocumented features of the Z80, the IS programmers were professionals!

Hahaha ... good for you guys!  

My folks in the games-industry side of things were always trying to push the hardware performance to the limit, and so the "undocumented" instructions were considered fair game to use in shipping products.

Those extra half-IX/IY opcodes are a lot more useful than the 6502's "undocumented" instructions.

When the CMOS 65C02 came around, very little software broke IIRC.

When Zilog made the CMOS Z80, thankfully the undocumented instructions still worked.

OK, so Z8S180 might be usable from a system point-of-view.  I wonder if the SD adapter code is also clean?


For some reason, I think that it might be interesting to run the Z8S180 at 6MHz, and see what kind of performance boost you would get over a 6MHz Z80.