Z80 Retro #24 - CP/M Introduction

CPMuseum on how to assemble an IMSAI 8080 kit:

George R.R. Martin explains why he prefers Wordstar 4.0:

The github repo seen in this video:

Related project hardware repos:

A Hackaday page for Z80 Retro! projects:

#Z80
#CPM
#BIOS
#homebrew
#retrocomputer

[herbertweinreich]

Thank you John for explaining CPM so transparently. I love my Apple / CPM systems even more now that I have converted them to access SD cards.

[Kimdino]

I knew there had to be folks out there that understood 'sed'. John, you are the first I've come across. ;)

[rancidbeef]

According to the Wikipedia entry for CP/M, the source for 2.2 was released under open source in 1997-98. And Lineo expanded the license to include other DR assets.

[rty]

I maintain all the S-100 bus computers at a computer miseum. We have about a dozen altairs and about 18 IMSAIs with a boatload of S-100 cards. Jave tons of VT-100s, decwriters, ASR-33 teletypes.
I work will all versions of CP/M even MP/M.
Back in the day i wrotr ALL my code in assembler on an IBM Mainframe since 1969. When i built my IMSAI (hated altair becuase front panel was octal - so unatural) i wrote a maimframe emulator so i could test my mainframe code. This saved me much valuable maimframe test time. I even had a kennedy 9 track tape drive connected to it as well!

[stefans]

I just love your channel. First thing to check everytime I youtube :)

[ShadowTronBlog]

As i recall the INP/OUTP put the 8-bit port address on both the LS and MS byte of the address bus. (The 8-bit port number is written to both address bytes). With a tight loop like you entered doing a INP 0xFF then an OUTP 0xFF you will see the 0xFFs on the MS address LEDs as well.

[PebblesChan]

Thanks for the great vid and here's a safety warning and a clarifications. #WARNING: watch out for Tag Tantalum capacitors which can become dangerous aerial fireballs!! # The best way to prevent them from igniting is to remove them or to use lower input voltages. (I had a 35V rated working voltage one fail at 30V a few days ago.) The 7805 regulators of that era are rated @ >1.0A, (peak 2.2A), often with TO-220 packages operating at 1A and TO-3 at up to 1.5A; the 78M05 variate is rated at >500mA (peak 700mA). The outputs from the chassis power supply are +8VDC (unregulated) and +/-16VDC (unregulated) to feed the onboard voltage regulators. The large filter capacitors of many old S100 systems have survived quite well, not losing capacitance or increasing ESR but a safety check is still recommended. Often these large capacitors have parallel bleeder resistors installed for safety. Be on the lookout out for old RIFA high voltage capacitors which fail with age! (It was years after the S100 era saw the introduction Chinese Crapacitors with a dud electrolyte formula that exacerbated the ubiquitous global capacitor problem). The heat generated by each voltage regulator is dependent upon their input voltage (from the chassis power supply) and the current being drawn; a minimum voltage drop of 2.5V is recommended between the input and output voltages (e.g. 8VDC input for 5VDC regulated, +/-16VDC for +/-12VDC ); years later LDO (Low voltage dropout versions were released allowing lower input voltages to improve efficiency and reduce unwanted heat generation.

[WilliamHostman]

The first two word processors I used were on CP/M... Perfect Writer and Wordstar.
I try to keep an emulator able to run Wordstar available for those times I need to have no-distractions putting text into bits.

[mikescott]

Makes me want to resurrect my IMSAI 8080. It hasn't been powered up in probably 40 years.
I don't think I'm brave enough to plug in immediately.
I would most likely pull the cards and start slowly on a variac.
Those tw 86, 000 uF electrolytics could make a big bang!
Also, when I was young and dumb (as opposed to now, old and dumb) I believed all ICs had to be in sockets and it's loaded with TI chips with silver plated leads, which are now black.

[BryanChance]

there might be a skeleton of a Univac in that basement..LOL

[grfulfox]

"In the mid-'70s, money was $200-300 a piece." That's some expensive money!

10:02

[StillChrist]

For the fun of it i decided to get very familiar with the ED editor, and compare it to Wordstar. For programming lines of code, i found ED to be better. For one, it loads a lot faster than Wordstar at original hardware speeds.. Thats important given that you can only run one program at a time. Two, you can use a custom Submit file to facilitate opening ED to whatever line, or block of lines you want. Like Batch scripts, Submit scripts take parameters. I changed the name of ED to EDIT so i could give ED to a .SUB script. ED 22 for example, could open my source code in ED right at line 22, very quickly, in just four keystrokes. This is especially useful given a language like C-Basic (from Digital Research) which would give you a listing of all the line numbers where there was a syntax error or something. ED was part of a nice little drvelopment environment, all tied together with .SUB scripts.😮

[zodakb]

Those old 7805 regulators were such a pain in the butt to me (in other hardware), that I went looking for an alternative. I found that RECOM makes a 78E5.0-1.0 which is a 5v switching regulator, 1A output, in standard 7805 pinout. It doesn't have a heatsink mounting hole, though. They take up to 28 volts input and more input volts doesn't mean more heat. It was a god-send when I wanted to add an ATTiny85 based light controller to my 24v powered 3d-printer. Not affiliated with them, other than as a satisfied Digikey customer.

[aghj]

I took s sip every once you said OK - now I'm wasted..

[streetfreakpatrol]

@30:49 INCORRECT - the BIOS/disk bootstrap loader (in a ROM chip) start/end address generally would NOT be movable and would reside at the very top of memory regardless of how much RAM you had in the system to ensure the BIOS system routine addresses would not move and always be at set addresses for the software (BDOS) below it to run them. This was to make sure the the BDOS did not have to work out the BIOS addresses to call BIOS system routines on based on the amount of RAM you had. If you Google the standard BIOS system routines like standard display output, disk access they are always at a set top memory address and never change. Not only that the character set bitmap lookup table would also be stored in this ROM which was accessed by the display hardware to generate characters on the screen. The display hardware would know where to look in the ROM for the bitmap e.g for the letter 'A' and use the bitmap data to draw dots on the CRT. It was important that the ROM/BIOS are did NOT change addresses so the display hardware would know a fixed address to use to do the character bitmap lookups.

[snarfusmaximus]

That 110V AC line you mentioned that is on the edge of the power supply PCB - I live in Australia, which has 240V AC (I don't recommend getting jolted at that voltage), and I own a Cromemco Z-1. It uses the same IMSAI chassis, front panel, and PSU as your machine but has a different overlay and uses a Cromemco backplane and boards. I purposely lifted that dangerous track off the edge of the PCB and rerouted it underneath using mains rated insulated wire to prevent me getting a shock. Now if only the front panel didn't have mains going to it. I haven't figured out an elegant way to fix that hazard.

[Kimdino]

John - A digression as not relevant to your Retro 80 but may be of interest.
Your talk of teaching the drive geometry to the CP/m system had my memory whirling and caused headscratching. I had an Amstrad PCW back in the day. These used Amstrad own 3" drives forcing the user to buy Amstrads own discs. I objected to this and unplugged the built in 3" drive and plugged a standard 5.25" drive in its place so I could use the cheaper and higher capacity 5.25" discs. This I could do because of the Shugart Standard interface for floppy drives, a similar thing to the modern SATA system.
So, it had me wondering me 'Why do you need to setup the drive geometry in CP/M"? Maybe because the Amstrad used a later version of CP/M i.e. version 3? Did Shugart come along later than CP/M 2.2? Or maybe my memory is playing tricks!

[melkiorwiseman]

Somewhere out in the garage, I have an old system which runs MP/M. It's probably no longer functional, but it was really good in its time.

[randallrouth]

I just discovered your channel.
I have watched you walk through your "reset" and "shadow" circuits.
Do you have the schematics to the IMSAI and can you walk through how it works. How is the processor paused, how is data written to RAM, how is the address advanced for deposit and inspect, how is the processor single stepped, etc.

[grahamnichols]

Proper computing. We suffered for our art. :)