Date : Tue, 12 May 1992 14:56:50 PDT
From : Raymond_J._Clark.Wbst311@xerox.com
Subject: *Big Board: Based CPM-80 Almost-A-Kit for Sale
The "Big Board" was a very popular CPM-80 system in the early '80s before the
IBM PC came out. It is virtually identical wire for wire to the Xerox 820.
I have 98s% of everything, just never built it. Everything in emaculate
condition.
$150 or best offer.
Big-Board which features:
Z80 CPU Board designed for 2.5MHz, most owners ran
at 4M. I have all 4M parts.
Z80 SIO (2 serial ports, One will be the console if you
talk to it first on booting)
Z80 CTC Timer Chip
Z80 PIO Parallel ports chip. I think 2 of 'em.
One used for Console Keyboard if you talk to
it first on booting.
1771 Floppy disk controller chip, single density. See
below- I have a double density upgrade kit.
Video On-board video controller generates 80x25
character display.
RAM 64K using 4116s. I have a 256K expansion
board, see below.
ROM Monitor source, both on 8" single sided single density
floppy and on IBM-PC floppy.
Documentation
All original documentation including mulitple
copies of the bare board to plan and document
any modification. Data sheets for all Z80 parts,
Z80 assembly language manual & reference
card.
State of assembly
All ICs socketed with gold machined contact
Augat sockets. 90% of passive components
installed. Careful record of assembly to date
following assembly manual and schematic
with red pencil. Beautiful job of assembling
by a perfectionist (me).
Single in-line sockets were used so you can cut and
jumper between the pins on the top side of the board.
Components included
Almost everything, two of some things.
Components missing
No Problems:
COM 8116 Dual Baud Rate Generator
Jameco has in stock for $4.95
74136
74LS151
Crystals: 14.31818, 20.0, 5.0688 MHz
(Need 32MHz XTL to run CPU at 4M)
Perhaps 10 misc. capacitors
Data sheets for almost everything, including but not limited
to all z80 parts, com8116, 1771, 2797. The rest is
standard TTL, 4116 DRAM, or 2114 SRAM.
Modifications
Modifications were planned for:
Run at 4MHz
Fix a video snow problem (faster character
generator and planned change
included. Has been tested elsewhere)
Change the video XTL frequency and clock
divider to get a wider display.
Patches for these may have been started on the
board, although I am 99% sure they were not. The
changes were very simple, and could be backed out
with a jumper or two using the schematics and
copies of the bare board. They will be documented
if done, and there are probably notes on exactly
what was planned, but no guarantees.
Single in-line sockets were used so you can cut and
jumper between the pins on the top side of the board.
256K expansion board.
You loose the lower 64K. I think the software that came
with it uses it for a RAM disk (floppy comes with). I have
a SIG/M disk which is supposed to have Trevor Marshall's
source to use it for track buffering.
Double Density Kit
Daughter board for 1771 socket to use 2797. No software,
although I assume it should be possible to find similar
software to do the blocking and deblocking and tweek it for
this chip. Data sheets included.
Floppy drives
Two Shugart 801 single sided 8 inch drives, brand new,
never out of box.
Video Monitor
Brand new, never out of box. Includes schematic. No case.
Comes with separate open fram 15v 1A power supply to
run it.
Keyboard
Very nice keyboard. Includes schematic. Parallel data
with strobe (which is what big board wants).
Software
Small C compiler, software to utilize 256K RAM board,
z80 assembler, misc disks with unknown S/W (On 8 inch
single density floppies). IBM-PC floppy with source for
ROM monitor, small-C, unknown other (it's been a
long time...).
Power Supplies
A Xerox 820 supply. Switching supply with +5, -12, +12.
I cannot say if this is adequate or not.
15v 1A for the video display.
You also need a 24 volt supply for the floppies.