CP-M Z80 home brew computer circuit board

Andrew Lynch lynchaj at yahoo.com
Sun Jun 15 09:36:23 CDT 2008

CP/M Z80 home brew computer circuit board

bfranchuk at jetnet.ab.ca bfranchuk at jetnet.ab.ca
Sat Jun 14 21:08:23 CDT 2008 

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Jim Battle wrote:
> Great, Ben!  I look forward to seeing your design.  Debug it, document 
> it, put up a web page, build PCBs, and offer to sell them at cost and 
> see how many grumbles you get.
Well when you think about it , I can down load a Z80 - CP/M emulator 
that is just as fast and
I can read emulated disks from my PC.  When I think CP/M I think floppy 
disk and I think
you still can get the floppy disk controller chips.

Hi!  Thanks Jim for the comments.  Please let me address the issues raised
by Ben:
If you look closely at the SBC design, you'll notice it has a feature even
better than a floppy controller -- it has a fully buffered IO bus!  It
contains all the Z80 signals brought out to the DIN 41612 connector.  The
peripheral bus adheres to the published ECB standard.
If you want floppy IO, the solution is simple -- just design one and attach
it to the bus!  I have already done this with my Disk IO board (IDE and
NEC765 FDC) which plugs into my home brew ECB backplane along with the SBC.
Assuming there is enough interest in these home brew SBCs, I hope to make a
PCB version of the Disk IO board. 
Yes, this SBC is a slightly modern variation of a vintage Z80 CP/M design.
I relaxed some of the traditions to make it affordable, reliable, and still
useful.  The P112, while an excellent design and a wonderful SBC, costs $165
for a kit when it is available.  I know of no other hobbyist Z80 projects
where one can purchase the PCB.
There are many Z80 designs available, however, without a PCB it means most
hobbyists will have to use temporary breadboards, wire wrap, or prototype
boards.  None of those lend themselves to long term reliable solutions --
especially for a wide range of hobbyist builders.
The SBC PCB is meant to be *low cost* and the *common* element of a home
brew computer with *simple* IO.  Adding unnecessary and complex IO
peripherals increases PCB area and cost, raises part count, and pushes away
the hobbyists it is meant for.
Selecting IO has to be done very carefully.  Not everyone who builds this
SBC wants floppy IO.  I have had numerous requests for many forms of IO
ranging from SCSI, IDE, floppy, CF, SD, USB, the Zilog peripherals, etc.
There is no solution which will satisfy everyone.

Implementing floppy IO can take on many variations and picking the FDC is
just the first of many challenges [FDC1793? NEC765? SMC9266? WD2797?].  What
about the data separator?  Few chips remain and viable sources are scarce.
Even integrated FDCs with built in data separators are not readily

Please remember, this is a *home brew* computer project -- a *real* Z80
running CP/M 2.2 on *real* hardware.  It is what you make of it.  If all you
want is a PC CP/M emulator then this project is not for you.
Thanks and have a nice day!

Andrew Lynch

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