SBC 80/20 Multibus

SBC 80/20 Multibus

Post by mlawso » Fri, 13 Mar 2009 10:34:31

Does anyone know of any SBC 80/20 Multibus card documentation or parts
are available anywhere? Mike

SBC 80/20 Multibus

Post by JW » Fri, 13 Mar 2009 18:31:10

On Wed, 11 Mar 2009 21:34:31 -0400 mlawson < XXXX@XXXXX.COM > wrote
in Message id: < XXXX@XXXXX.COM >:

Damn, I thought I might still have that one, but no. All I have is iSBX
specification, Multibus specification, SBX311, 86/14/, 86/30, and 86/12
manuals. You might try here:

As for parts, what are you looking for?


SBC 80/20 Multibus

Post by noratec » Sat, 14 Mar 2009 05:23:30

I have some info. What exactly are you looking for? Email me at this
username at gmail.

mlawson;858080 Wrote:


SBC 80/20 Multibus

Post by mlawso » Sat, 14 Mar 2009 11:25:02

What I'd like to find are some schematics, along with some working
boards and motherboards. There are several sites that have .pdf files of
the documents for S-100 parts, and I am hoping there are the same things
for the multibus architecture. Mike

SBC 80/20 Multibus

Post by noratec » Sat, 14 Mar 2009 12:25:47

The SBC docs (mostly paper) and boards are not so easy to come by. Herb
has the best info I've seen online so far. (see JW's post)

The SBC80/20 needs a multibus I backplane and power supply. Since it
uses the 8080 CPU, the power supply needs to delivery both plus & minus
5V as well as plus and minus 12v. So an SYP310 or later chassis won't
work. Intel didn't use the 8085 until the SBC80/24.

You can put several SBC (single board computers) in a chassis. Sort of
like mutliple cores :) And also add more RAM and peripheral
controllers, like the ISA bus on early PCs.

The major chips on the 80/20 are two 8255s (parallel port interface)
one 8254 timer, one 8251 uart and one 8259 interrupt controller.

Firmware is the next issue. You will need to write your own unless the
board still has the original Intel monitor eproms (probably 4 x 2716s)
or the developer kept some of the monitor code.

The dasm80 disassembler will run in a CMD window on XP if you can
extract the data from the eproms in Intel Hex format. You may still be
able to find an 8080 assembler on (such as

Hope this is helpful.


SBC 80/20 Multibus

Post by westo » Sun, 15 Mar 2009 12:52:58

S-100 and iBus are completely different except for their common
factor - the 8080 signalling standards. I believe I have 80-10
documents buried somewhere. A better answer comes with more
information on what you want to accomplish.

Another suggested it needed -12 volts. I believe it also needed -5
volts. The multibus also had to provide other essential functions
including power on reset and watchdog timing.

SBC 80/20 Multibus

Post by mlawso » Mon, 16 Mar 2009 06:01:00

What I want to accomplish is to homebrew one. Many years ago I
wirewrapped a TRS Model 1 PC and had a blast. Yep, I'm an old fart! And
it's a nice little hobby. I'll probably re-configure it to support a
Z-80. I also worked with my first multibus products when I worked for
Dictaphone back in the late 70s. We had a product that used the multibus
board so I have a bit of knowledge of them. Thanks, Mike

SBC 80/20 Multibus

Post by westo » Mon, 16 Mar 2009 17:45:56

Now I am completely inspired. Somebody who actually wants to learn
something rather than shotgun computer boards and call himself

Unfortunately, the hardware configurations of the Z-80 and 8080 are
different. And the Z-80 had a slightly larger instruction set.
Closer to the Z-80 was the 8085. I also designed hardware and wrote
software for that computer chip.

Because I am inspired, I dug through those piles from history. I
found multibus manuals for the 80/10 (8080 microprocessor) and 80/24
(an 8085 micro).

8085 was closer to the Z-80 (including no -5 volts required). But
Intel never got that chip to work fully correct. However Intel also
realized that the 8085 was wasting time playing catchup with the
superior Z-80. So Intel jumped forward to promoting the
simultaneously developed 8086 - which became the basis of what?

Zilog never recovered by trying to promote Z-80. Eventually Zilog
became part of Exxon when Exxon was foolishly doing what business
school graduates recommend. Z-80 was the first of many companies that
would attempt to challenge Intel's greatest power - its abilities to

One neat feature of the 80/xx series were peripheral ports that
could be changed simply by replacing chips in 16 pin sockets. For
example, I reconfigured one design using especially powerful drivers
from Silicon Solid State Scientific (if I remember) that were more
powerful and transient hardened AND that were pin for pin compatible
with TTL chips for those sockets.

If I remember correctly, those multibus cards required better
regulation on its power supply as well as a master reset provided by a
multibus one backplane.

Eprom - largest was a 2732 on 80/10 and 2764 on 80/24. But again,
for memories over twenty years ago. Eproms from that other computer
would not work. Code must first setup peripherals unique to the
Multibus card. For example, Intel used its own serial port chip.
Many computers used a better (and different) serial port chip. Setup
required different bytes in different registers. Not that I am trying
to discourage you. But those multibus cards require writing code and
burn those newly programmed Eproms.

SBC 80/20 Multibus

Post by mlawso » Mon, 16 Mar 2009 20:59:31

estom wrote:
Well, truth be told I already have a Z-80 design done that I plan on
using to control my model train set. I have a Z-80 assembler that runs
under Windows and I plan to take the compiled code (in a hex file) and
read the file into a Basic program for output to the parallel printer
port. That will connect to the Z-80 system directly into memory. The
printer port strobe signal will write the byte into memory and also
advance a series of binary counters to the next memory location. I am
using the BUSRQ control line to switch the address & data bus from the
Z-80 to this input method. Then, once the code has been transfered,
release the BUSRQ and let it rip.... I hope it works. I'm going to start
wiring it up this summer. Mike