Z84c40 <=> Z84c42 compatibility query.

[Nem Ster]

Hi Folks;

I have debugged by board. Assembly is great and all the chips are in. Everything looks good. BUT...In my haste to order and assemble I have inserted a Z84C40 instead of the Z80C42  (Dumb A.. me).

Question: Is there a simple way to make the Z84c40 work ? or are they so different that I have to order a Z84c42 ? Thanks in advance.

/Gabe

[Jon Langseth]

You will have to do some cobbling based on close attention to the datasheet. Internally, the SIO/0 and SIO/2 are more or less identical. The difference is in the bonding options. To quote the datasheet:

> The constraints of a 40-pin package make it impossible to bring out the

> Receive Clock, Transmit Clock, Data Terminal Ready, and Sync signals for

> both channels. Therefore, Channel B must sacrifice a signal or have two

> signals bonded together. Because user requirements vary, three bonding

> options are offered:

> * Z80 SIO/0 contains all four signals, but TxCB and RxCD 

>  are bonded together (Figure 101).

> * Z80 SIO/1 sacrifices DTRB and keeps TxCB, RxCD and

>  SYNCB (Figure 103).

> * Z80 SIO/2 sacrifices SYNCB and keeps TxCB, RxCB 

>  and DTRB (Figure 105).

As I (naturally) have not tried this myself, I'll give no guarantees, but it seems to me it should be doable. Without looking too closely, it seems to me your area to focus are the four pins 26 through 29. Hopefully you've used sockets, allowing you to make an adapter that sits between the board and the SIO/0.

For ease of availability, I've uploaded the Zilog Z80 Family Peripherals data user manual to http://linc.no/dl/linc80/doc/um0081.pdf

[Nem Ster]

OK, so after some tinkering it was all me. It works beautifully !!! :-)

Lessons learned:

1. Always look in the old "chip drawer". You'll find a Z8442A SIO/2 from 1982, that the test engineers tossed...

2. Don't assume this computer uses a 10Mhz crystal as this really messes up the BAUD rate ;-)

3. Always order from DigiKEY.

4. A Transcend 32Gb UDMA 400x compact flash does not boot.

5. a 340Mb IBM CF Microdrive does not boot either...shrug.

..

5. Keep having fun. CP/M is next. Now to find a CF card that works..

/Gabe

[Steve Cousins]

I think we all have a list of lessons learned from these projects.

The problem comes when we learn the same lesson again :-(

Steve