Emailing CP-M Z80 home brew computer circuit board.htm
lynchaj at yahoo.com
Tue Jun 17 16:51:38 CDT 2008
Emailing: CP-M Z80 home brew computer circuit board.htm
bfranchuk at jetnet.ab.ca bfranchuk at jetnet.ab.ca
Tue Jun 17 11:09:33 CDT 2008
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> Have you ever used 8"SSSD to do anything that required space? There
> enough space to run a disassembled version of the BDOS through ASM
> unless you have at least two drives and don't mind doing cleanup.
I never could run the CP/M system I was using for more than 30 minutes
the floppy stepper sticking. That was fun working with it. Still how do
stuff from a floppy ( or file online ) to a CP/M system with no
external I/O devices?
> Yes you can roll your own data sep it only needs three ttl packages.
> With all the other hardware needed for the 765 case you end up with at
> least 10 chips
> though If you willing to miss a few features it's been done in 7 plus
> the FDC
> and that doesn't include the bus side of the FDC interface.
That I would like to see.
> Kicad for linux there are other like cadstd for winders.
> Of course the last 2901 design I'd done in the early 80s was
> with paper and pen! It's doable that way.
I still am using paper & pen. Mind you I have to buy JAPANESE pens
since the quality of the USA stuff is all cheap Chinese imports.
Now that I have a serious cad program - DIPTRACE on order
I think I will put the design in hardware.
> FYI using 250nS eproms will make it terminally slow unless
> you do two things, use a wide microword 64bits or more and
> pipeline the address and decode so you can work right to the
> eprom Tacc minimum limit.
I got that covered if I read the 2901 data sheets correctly.
I will be using a 6809 style memory cycle optimized for
D-RAM access and clock the 2901 in 4th phase of
the memory cycle. This is retro computing project for the feel
of the late 1970's not using a 8 bit CPU. I am aming for
a 800ns memory cycle and the slow access of micro-code
is not a problem. The only thing pipelined is the next memory
cycle - Read/Write/Refesh and the default is refresh while
doing the the 1st cycle of op-code decoding. The front
panel does RUN/STOP, Single Instruction,Address Load,
I can answer the question on how to get programs and data into and out of
There are three ways with the basic SBC;
1) XMODEM at the CP/M prompt
2) Intel Hex format transfer at the RAM Monitor prompt and
3) burn your own EPROM with the supplied image or your own custom disk image
(utilities are on the website)
Here is a little background on the N8VEM SBC design principles
The N8VEM SBC is meant to be flexible and low cost. If you start with the
PCB only, you can minimize cost by not installing unneeded functions such
2) 8255 PPI and parallel port connector
3) ECB Bus transceivers and DIN 41612 connector
You can also substitute some parts to reduce cost. Replace the 1Mx8 EPROM
with a 128Kx8 27C1001 is a drop in replacement.
Scrap and salvaged parts can be used directly or with minor modifications.
All the chips are commonly available plain TTL and can be substituted.
All of the other components can be substituted if you know what you are
Scrap 29C020 Flash ROM chips (PC BIOS) can be reused with a simple shim
Most likely 128Kx8 SRAM parts with a shim socket can be used but I haven't
tested it yet
Installing and running CP/M 2.2 OS is strictly a convenience and an option.
Any generic CP/M application should work.
The RAM and ROM drives are lightning quick and silent. You'll never see a
hung stepper motor with SRAM!
The SBC boots into the RAM monitor so you may never need to run CP/M at all
if you don't want to.
The system I built is rock solid. It runs for hours doing things without a
sound or glitch. I used some CMOS components so the SBC runs cool.
Power supplies are easy and cheap. Use spare ATX/AT PS or your own with the
common Molex drive connector.
Of course, all the hardware and software details are fully published and
with datasheets for all the components.
Except for the EPROM there are no custom or programmed devices at all. All
components are bog standard common 74LSxxx TTL and LSI peripherals.
It is designed to be built with low cost tools and simple test equipment
such as 25W soldering iron and VOM.
EPROM programmer, logic probe and/or oscilloscope are useful but optional.
You can easily write your own replacement software like a FORTH kernel or
custom Z80 boot code if you'd like.
The EPROM on the N8VEM site is strictly optional and I actually discourage
people from using the pre-programmed part.
Write/burn your own and save $$$ on construction.
With the low cost PCB available and using standard low cost components
anyone can build their own SBC for low cost.
You can add the features you like later on and even expand the system via
the ECB to be a full blown microcomputer.
Once a few of these systems get built "out in the field" I would like to
start a challenge to see who can build an SBC for the least cost.
Those with a well stocked junk box or access to scrap PC electronics would
have an advantage of course.
Compared to a design it yourself using wire wrap/prototype
boards/breadboards, this SBC PCB will save you time and money on
Manufactured PCBs are also more reliable than temporary construction methods
in the long term.
It will be fun to make, useful, and educational.
Thanks and have a nice day!
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