SWTPC 6800 and Percom Floppy Controller

Mike Douglas deramp5113 at yahoo.com
Sun Jan 12 07:55:01 CST 2020

I’ve been able to complete the system running under the MiniDisk+ PROMs and added several programs like BASIC and an assembler to the disk. It all works together, but operations don’t integrate with each other very well.

With much thanks to Bill Sudbrink, I also obtained the source to Percom’s MPX PROM so I was able to create a system running under MPX. Bill also had several of the programs (in S19 format) that would have been distributed with MPX, so I’ve got a pretty representative Percom MPX system up and running now. This setup, in turn, is pretty darn slick and well integrated for its day. It’s a lot like a Northstar DOS system, but a bootable disk is not required to get started since the OS is in PROM. Add the fact that the standard SWTPC configuration with MIKBUG or SWTBUG made it simple to get programs into RAM via the serial port (e.g., S19 records from papertape, cassette, or today - a PC) and it’s easy to build up a disk from scratch.

I’d still like to flesh this system out a bit more, so if anyone has any Percom disks or software archived in any format on a PC, let me know, thanks!


> On Jan 7, 2020, at 6:44 PM, Mike Douglas <deramp5113 at yahoo.com> wrote:
> I’m restoring a SWTPC 6800 that includes the Percom LFD-400 floppy controller. This controller goes on the SS-50 bus instead of the SS-30 bus where the SWTPC controllers installed. The standard Percom MiniDOS PROM is installed, and the other two PROM sockets have a third party extension called “Minidisk+”. This was made by a company called Cer-Comp. These PROMs are instead of Percom’s own “MiniDOS PlusX (MPX) PROM. 
> I’ve got the system working, and I can use Minidisk+ to save and load files, but I know I’m missing some nuances of command parameters. I don’t have any sort of documentation for Minidisk+, so before I go figure it out by disassembling the PROMs, does anyone have any sort of documentation for Minidisk+ by Cer-Comp for the Percom LFD-400 floppy disk controller?
> Also, I’d like to burn the MPX PROM as an option. Does anyone have the MPX PROM or the source code for MiniDOS PlusX?
> Mike

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