Starting for Z80 card

APPLE II using 6502 CPU and there are another 8 bits CPU Z80 is one of famous one too.

In fact, APPLE II can use both of CPU Z80 and 6502 but, It was almost forgotten technology how to applied it on APPLE II.

Hence, I started to make Z80 card and it will work as a softcard for CP/M.

Used Z80 CPU and some chips.

Major control chip will use a CPLD to act as Softcard and started wiring.

Wiring always hard job but, but have to check all of lines to make sure to avoid mistake connection.

I was took long hours and needed adjust wires to fix my mistakes.

I set chips and added some more wiring for proper emulate the Softcard.

I did research about the softcard and could learn about the DMA works and RDY and the trick of timing for Z80 CPU.

My plan is several steps,

First, I want make it run the CP/M OS.

For this I will apply some slow Mhz and try to make it run as Softcard.

I think that it is possible to make it run 1Mhz and it would be easier than other faster speed.

Then Try other faster speed.

2Mhz is original softcard and at least have to reach this speed to make feel same as what I experienced by the CP/M by softcard.

The final softcard make it run as 7Mhz..

It is the maximum possibility with softcard design I guess.

Anyway, there is a reference of 7Mhz CP/M.

http://www.applefritter.com/?q=content/z80-softcard-able-run-7mhz-faster-stock

It looks very interesting to me. but, I don't understand fully about the tricks.

Anyway, Let me see if it works.

Thanks