I was staring at an SBC I have here with a 6MHz Z-80, some ROM, some RAM,
and a 26-pin off-board bus for some Z80-PIO boards (this thing was built
as a multi-parallel-printer switcher). I've been musing about what it
would take to boot CP/M up on this.
For user I/O, I was planning on a console serial port and a
emulator. I have IM6402s on hand, but I'd be interested in hearing if
certain other chips are preferred, based on what BIOS code is floating
around out there. I also have a 16550, but I don't think I have any
Z80-SIO chips handy.
For mass storage, I was planning on either Compact Flash or an SD card.
I think I've seen both as I googled around for modern SBCs. Any of the
media I have lying around is plenty large enough (I even have some 4MB
CFs and a 2.5MB full-sized PCMCIA flash card on hand).
I am a little unclear, though, about how traditional CP/M systems
were set up for ROM and RAM. Was it common to use a "shadow ROM"
in low mem at reset, then have the BIOS live at the top of memory?
How did 64K RAM CP/M machines handle the BIOS? Did they temporarily
ghost the ROM on top of RAM until some bit of code could read ROM
and write RAM then bank out the ROM? Since I think I "need" at
least 48K of RAM, I was planning on a pair of 62256s. I could easily
do 56K of RAM low and 8K of ROM high, I think, unless there's some
other arrangement that's obvious to try for a simple design.
I've never tried writing a BIOS for a CP/M machine, but my understanding
is that things are modular enough that once you know what I/O chips
you have and at what I/O addresses, for a straightforward, non-clever
design, the coding is equally straightforward and non-clever (but please
feel free to enlighten me if otherwise).
Thanks for any tips, especially from anyone on the list who has ever
rolled their own CP/M machine.
Ethan Dicks, A-333-S Current South Pole Weather at 4-May-2008 at 19:40
South Pole Station
PSC 468 Box 400 Temp -74.2 F (-59.0 C) Windchill -105.4 F (-76.4
APO AP 96598 Wind 7.4 kts Grid 77 Barometer 691.6 mb (10194
Ethan.Dicks at usap.gov <http://www.classiccmp.org/mailman/listinfo/cctalk>
Funny you should mention the subject, I am working on a very similar
Last year, I made a completely home brew Z80 computer with prototype boards.
It is a fun project and you can definitely build your own CP/M computer from
scratch. It really is not that hard.
This year, I am remaking the design using manufactured PCBs.
I recently got my first batch of prototype PCBs and have been building up
and testing them.
So far, I have gotten the CPU, ROM, RAM, UART, and most of the glue logic
working and tested.
It is not complete yet as I still need to wring out much of the hardware and
have not even started on the PPI or RTC.
However, last year I was able to boot the previous system into its monitor
and even boot CP/M.
CP/M used a 32K ROM drive for drive A:, a 448K RAM drive for drive B:. I
implemented an IDE port and a hard disk for drive C:.
Those all worked pretty good. I built but never tested a floppy drive
The whole system is pretty simple, uses plain 74LSxxx chips, no programmable
parts (except the EPROM) or hard to get parts.
No SMT or funky technologies, just plain through hole DIP chips.
I have all the software and am presently going through the library
reinstalling it on the new system.
So far, I have most of the easy stuff working. I do have the RAMless
monitor working and next will be the regular monitor.
Finally it will be the CP/M system and the RTC software.
Anyway, if your interested, I am keeping a small Google group of files and
Hopefully, this request is clear enough to be understood. Both the
software and the hardware portion of the questions are independently
important, so please answer one aspect even if you can't help with
Over the past 30 years of using PDP-11 software (RT-11 over 95%)
and hardware, I have never had occasion to use a Unibus system with
more than 256 KB of memory (such as a PDP-11/34).
I would appreciate help in understanding the Unibus Map hardware which
(if I understand its purpose correctly) is to convert 18 bit addresses given
to a Unibus controller into 22 bit addresses for real physical memory for
systems like a PDP-11/84 and perform DMA from / to the hard drive.
Also helpful would be an explanation of the related software used under
RT-11 along with exactly where the Unibus Map hardware is located
on a real DEC system (on the CPU board I presume) since the identical
CPU board is used for both the Qbus and the Unibus with both the
PDP-11/84 and the PDP-11/94.
DO NOT READ THE FOLLOWING if you don't use RT-11!!!!!!!
By way of context, I have successfully modified the HD0: device driver
originally written by John Wilson which obviously executes ONLY under
E11. Last week, John mentioned in a private e-mail that it is possible to
direct the HD0: "controller" (all references to hardware in quotes refers
to E11 software) to ignore the "Unibus Map hardware". Since I execute
under E11 using Qbus emulation in order to stay totally compatible with
the real DEC PDP-11/23, PDP-11/73 and PDP-11/83 systems (all Qbus
and all with 4 MB of physical memory) which I have available for comparison
testing, user buffers in physical memory above 256 KB are often a situation
which can't be avoided.
Consequently, it had always been a high priority to have a 22 bit device
for HD0: under E11 BECAUSE HD0: is TWICE as fast as MSCP (DUX.SYS
device driver). In addition, I have also been able to write code that
overhead of using the HD0: device driver which makes HD0: FOUR times as
fast as MSCP and also allows for direct access of 2 TB of disk space via a
32 bit block number. Since I have an immediate application for a data base
of 32 GB (I have a disk drive of 160 GB, so 32 GB is only 20% of its
although under RT-11 15 years ago in 1992, 32 GB would have been only a
dream), the code which I have written will actually be used quite soon.
However, I would very much like the HD0: device driver to be able to execute
under both "Qbus" and "Unibus" hardware. And while I can test the code for
a "Qbus" and for a "Unibus" without a "Unibus Map", I am not clear about
what is required for a "Unibus" with a "Unibus Map" such as a PDP-11/84
running under RT-11.
Megan are you still watching the list? Allison, if you can't answer,
but Megan help? Is anyone else familiar enough with the "Unibus Map" that
you can suggest what RT-11 actually needs to do with the "Unibus Map"?
A solution is to check the "hardware" configuration and refuse to allow the
HD0: device driver to LOAD or .Fetch if the modified version is not
executing under "Qbus hardware".
By the way, if anyone who is thinking of a controller for the Qbus which is
able to use SATA drives, I would be happy to modify an RT-11 device
driver to an HD0: type device that is able to handle drives up to 2 TB
in the same manner that DU(X).SYS can handle drives up to 8 GB.
If you attempted to send a reply and the original e-mail
address has been discontinued due a high volume of junk
e-mail, then the semi-permanent e-mail address can be
obtained by replacing the four characters preceding the
'at' with the four digits of the current year.
I'm trying to use simh to create an RT-11 bootable RX50 disk and am
following some instructions posted by Megan Gentry a while ago. I've
created the disk image but am having trouble making it bootable. The
copy/boot command claims it can't find the RT-11 image but it is
clearly on the floppy (du0). Any idea what's going wrong?
RT11XM.SYS 106P 20-Dec-85 DU .SYS 8P 20-Dec-85
TT .SYS 2P 20-Dec-85 PIP .SAV 30P 20-Dec-85
DUP .SAV 47P 20-Dec-85 DIR .SAV 19P 20-Dec-85
RESORC.SAV 25P 20-Dec-85 EDIT .SAV 19P 20-Dec-85
MACRO .SAV 61P 20-Dec-85 CREF .SAV 6P 20-Dec-85
LINK .SAV 49P 20-Dec-85 LIBR .SAV 24P 20-Dec-85
FILEX .SAV 22P 20-Dec-85 HELP .SAV 132P 20-Dec-85
BATCH .SAV 26P 20-Dec-85 FORMAT.SAV 24P 20-Dec-85
SETUP .SAV 41P 20-Dec-85 SPEED .SAV 4P 20-Dec-85
DATIME.SAV 4P 20-Dec-85 LET .SAV 5P 20-Dec-85
SPLIT .SAV 3P 20-Dec-85 CONFIG.SAV 7P 20-Dec-85
SWAP .SYS 27P 20-Dec-85
23 Files, 691 Blocks
95 Free blocks
.copy/boot du0:rt11xm.sys du0:
?DUP-F-File not found DU0:RT11XM.SYS
>Subject: TU-58s (was Re: Some progress with my PDP-11/73 system)
> From: "Ethan Dicks" <ethan.dicks at gmail.com>
> Date: Wed, 11 Apr 2007 21:54:24 -0500
> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>On 4/11/07, Jerome H. Fine <jhfinedp3k at compsys.to> wrote:
>> But I once had a project that
>> used a real DEC TU-58. Not the fastest "random"
>> access device!!!!!!!!!!!!!!!!!!
>They work better as "sequential" access devices - being long and thin
>and travelling in one dimension, go figure. We used to optimize file
>order on our console TU58s to speed up the boot times on our 11/725s
>and 11/730s. Since the file order doesn't change, one just builds a
>TU58 with EXCHANGE with each file following the other. The console's
>8-bit-micro must cache the directory block, since the tape didn't whip
>back to the start between each file.
>Using unaltered console tapes from DEC resulted in, IIRC, about 15
>minutes from turning the key to booting the hard disk. Replacing that
>tape with one of our own devising shortened that pre-boot time to well
>under 3 minutes.
>I'd hate to rely on a TU-58 and no other block-addressable media on a
>PDP-11, though. I survived a PDP-8 with a TD8E and TU56, but it was
>somewhat tedious (cool to watch, though). TU-58s weren't as cool,
So happens one of my "small" pdp-11s uses a Tu58. the system is a BA-11V
with an 11/23 256k of ram, DLV11J and MRV11 rom(boot). Takes 10 minutes
to boot, setup VM: then copy key files to and reboot. After that it's
pretty decent even if I have to access a file on tape.
Everytime I runs it with a bunch of kids of the current PC generations
they go gaga and comment on how slow then I explain the amount of ram and
storage then they are amazed it can be a functional machine with so little.
They can't imagine a useful machine with 32kW of ram and 256kb of storage.
On the flip side I've used that same Tu58 to bring up iron that had no
removable storage. It's slow but very dependable.
heres a link to some lead solder
On 10/2/07, Zane H. Healy <healyzh at aracnet.com> wrote:
> At 11:37 PM +0100 10/1/07, Tony Duell wrote:
> >For the first part, I'd offer to do it for you, but it would be illegal
> >to do so. Owing to our totally daft laws, (a) I'd have to use lead-free
> >solder, which I don't have, don't trust, and am not set up to use and
> How hard is it to work with lead-free solder, and is it becoming a
> problem to get traditional solder in the US? I've been meaning to
> pick up a few rolls. As I'm still using a roll purchased in the 80's
> from Rat Shack for building a couple things for my VIC-20, I haven't
> been going through it that fast. Though I seem to be using it more
> often now than.
> >it has been said that if an enthusiast (specifically a model engineer,
> >but it would apply here too) does jobs for others, then his workshop
> >becomes a workplace and is covered by all the daft health-and-safety
> >rules that I have no desire to get involved with, and which quite
> >honestly, would stop me from getting on with things.
> Does it count as a job if you don't take payment?
> | Zane H. Healy | UNIX Systems Administrator |
> | healyzh at aracnet.com (primary) | OpenVMS Enthusiast |
> | MONK::HEALYZH (DECnet) | Classic Computer Collector |
> | Empire of the Petal Throne and Traveller Role Playing, |
> | PDP-10 Emulation and Zane's Computer Museum. |
> | http://www.aracnet.com/~healyzh/ |
Just a quick introduction - besides being the guy who can't make his IBM
6904-20 Lighted Programmable Function Keyboard work on a serial port and
writing a TCP/IP stack from scratch that runs on a PCjr, I am also a
moderator at The Vintage Computer Forums web forum (
http://www.vintage-computer.com/vcforum/ ) . Some of you are regulars
there too, but it is more PC and smaller computer oriented than most of
you on this list are.
We have many of the same problems with well known auction sites that
many subscribers here have. We also have enough traffic in our 'for
sale' section of the forum to finally warrant a more structured auction
type service. So we are happy to announce "The Vintage Computer and
Gaming Marketplace" at http://marketplace.vintage-computer.com/ .
The idea is give vintage computer collectors an alternative to your
favorite big site that is more targeted to our specific interests. It
is simple to use, it supports auctions and normal fixed price sales, and
there is none of this sniping bogusness that happens on eBay. Best of
all, it's completely free to use - no listing fees.
Thanks for reading,
PCjr nutcase and soon to be TRS-80 Model 4 nutcase
Have a working Intel Above Board Plus 8 with 2MB RAM and would like to
populate it to the full 8MB. It will take 120ns or faster 1mbit chips
-- but where can one find that kind of thing nowadays? Are those still
commercially available or am I going to have to scavenge them from
Manual lists acceptable part numbers like:
...etc but google searches haven't been very fruitful (that is, the
pages returned when I search for IC part numbers don't return vendors
with plain pricing/availability info).
I just want a few tubes of these to populate the board, I'm not looking
for a box of 'em :-) Any pointers?
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
Anyone collect and/or need parts to the AT&T Unix PC? I've got a pile
of systems I dismantled over a decade ago, and don't really want or know
how to put back together. I bought them "new" as surplus by the pallet
at the time, and about half of them were defective with only displaying
horizontal lines when turned on. The monitors are perfect, I also have
the 20Mb MFM drives and 5.25" drives, as well as the mainboards,
plastics etc. I'm not sure exactly how many and what I have yet, but
checking for interest here. Please reply if these are of interest at all.
Any suggestions on the line problem?
Time has come to clear out a major portion of the stash. At my
age I will never get around to all of the projects. The
following is a partial listing of what is available. I will add
to the list as stuff emerges from the pile. Make offers, cash
or trade. Pickup only in Guntersville, AL, USA.
mVAX II (BA-23) several
mVAX II (BA-123) several
Vector 3 with mindless terminal
DynaByte 8/2 with 8/4 drive box 2 ea.
WellFleet (Bay) Router 3 ea.
Micom Marathon 1K
TI Travelmate LT-220
Hyperian portable PC
HP Apollo 710
Atari 1041ST w/monitor
Teletype model 43
various DEC Qbus card cages for PDP-11
power supply, blower and etc for RM-03
The following needs to go to someone that can make them available to the
A lot of VMS gray wall books
A lot of VMS orange wall books
A lot of component (IC, diode, transistor) manufacture's data books