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Cromemco SCC and Board Testing

Posted on by Graham

The Cromemco Single Card Computer (SCC) design dates back to 1978 and this particular unit appears to have been made in 1978 or early 1979.

It has a Z80 processor running at 4MHz, 1kB of RAM, space for 8k of 2716 ROM, three parallel ports and one serial port.

The board was ROM-less but the binaries for the usual ROM set, MCB-216 were available online. These ROMs provide a monitor and 3k basic.

This means that with the addition of a terminal it’s possible to have a single card capable of executing programs that can exercise the S-100 bus.

I burnt the code into a couple of EPROMs, hooked up a terminal, and gave it a whirl. It fired up as if 45 years meant nothing. It starts up basic to start with but QUIT sends it to the monitor and B in the monitor sends it back to basic.

Programs can be saved to memory including to EPROM on particular Cromemco boards. They can also be saved to or read from the serial port.

The Monitor includes a memory test. I used it to check out a number of memory cards, with some success.

The Cromemco 64KZ appeared to be working fine. One board didn’t work because it expected pSTVAL to be driven and the SCC does not drive it. This was when i started to understand that the S-100 bus was not as “standard” as i had thought.

The main outcome was that i had a Cromemco memory card that was likely to be functional.

Sorcerer ROMPAC Basic Games on CP/M

Posted on by Graham

There were a number of games on the Sorcerer disks that fired up fine, but there were a large number that did not.

I got some help from Alan Laughton (Microbee Technologies) to work out what was going on. He spotted that the files contained basic. They were com files – so quite different from the basic files that you would load into the disk basic.

Browsing through the manuals and other data, it became clear that the ROMPAC BASIC work area had been set up in such a way as to allow programs to be saved and loaded with CP/M.

The ROMPAC basic has a lot more memory available to it than the disk basic. It doesn’t waste space on the interpreter or the operating system.

The first entry in the com file is a jump to the warm start area of the basic ROMPAC. This failed on my machine because i had no ROMPAC.

What i did have, though, was a 8k S-100 RAM card (Solid State Music MB6) which i could locate at the same address as the ROMPAC at C000.

The card, predictably, failed the Sorcerer Monitor RAM test, but the offending IC was found and replaced.

I tested it out by using ddt to load the ROMPAC which was moved up into the RAM card. Following reset, the “RAMPAC” was found and basic fired up.

“bye” at the basic prompt returned to the Sorcerer monitor and GO BC00 started CP/M again. One of the previously failing com files was loaded and sure enough it ran!

After that, i wrote a very short program that replaced the ddt step. This allowed another 23 games to execute.

I’ve since created to couple more which load the development and word processor ROMPAC code into the RAMPAC.

The memory card had a facility to write protect the contents, so i added a switch to the expansion unit to enable it.

Transferring ROMPAC Basic Programs from CP/M to Tape

Posted on by Graham

Some of the basic games that have been stored as CP/M com files are missing from the sorcerer archives at Microbee Technologies (Alan Laughton is the curator) so i went through the process of transferring them back to audio files.

These were translated to wav files as follows:

  1. At monitor GO BC00 to boot up CP/M.
  2. Load the basic rompac (LDRAM).
  3. Reset – starts basic.
  4. Bye to return to monitor.
  5. SE T=1 to set 300 baud.
  6. GO BC00 to boot up CP/M.
  7. Load up the game eg A>LAIR to load up LAIR.  This starts up the ROMPAC basic.
  8. Load up Audigy on a PC.
  9. Set recording gain to max and the input to mono.
  10. Connect LINE IN on PC to AUX on Sorcerer.
  11. Start recording and enter CSAVE LAIR.
  12. When the sorcerer comes back with READY stop the recording and trim if necessary.
  13. Apply a good 20dB of gain to maxout and square up the waveform.
  14. Export the audio to a wav file.

Check as follows:

  1. Connect the PC LINE OUT to the input of the external amp.
  2. Connect the external amp output to the EAR input of the Sorcerer.
  3. Set Audigy playback volume to max. 
  4. Watch the EAR input with a scope and back off the Audigy volume until the waveform is clean and square.
  5. CLOAD LAIR.
  6. Hit play on Audigy.
  7. The title should be shown in less than 30 seconds.
  8. By the time the audio is complete, the sorcerer should say READY.
  9. RUN and enjoy.

If you want to do another then breakout with ^C, BYE to return to monitor and GO BC00 to boot CP/M.