Copyright 2016 Eric Smith spacewar@gmail.com
mds-fw development is hosted at the mds-fw Github repository.
Before IBM PC compatible computers became ubiquitous, microprocessor vendors sold proprietary microprocessor development systems. Intel's early offerings included the INTELLEC 4/MOD 4, INTELLEC 4/MOD 40, INTELLEC 8/MOD 8, and INTELLEC 8/MOD 80, for the 4004, 4040, 8008, and 8080, respectively. In 1976 Intel introduced the MDS 800 Microcomputer Development System, which was the first system to use Intel's general-purpose bus standard, later known as Multibus, and Intel's first system to support floppy disks, using the MDS-DOS subsystem and ISIS operating system. The MDS 800 was normally used with a serial terminal such as the Beehive MiniBee, sold as the Intel INTELLEC MDS-CRT.
In 1978, Intel introduced the INTELLEC Series II MDS, which used an IPB-80 main processor board (8080-based). All Series II models other than Model 210 also included an integrated 8080-based IOC (I/O Controller), providing a built-in video terminal and a single-density floppy controller (not used in all models). Later models replaced the IPB-80 main processor board with an 8085-based IPC-85.
Later Intel introduced the Series III MDS, which was a Series II with an 8086 processor board (RPB-86 or RPC-86) added, the iPDS, which was a more compact, portable development system, and the Series IV, which was significantly different.
This project contains reverse-engineered "source code", with varying degrees of completion of the reverse-engineering. However, all of the source code is verified to assemble to the original binary. The makefile in each subdirectory has a "check" target which will compare a SHA256 hash of the assembled binary file to the hash of the original firmware.
This includes both 8080 code and 8041 UPI code, which are intended to be assembled using the Macroassembler AS. Due to the use of long identifiers, it may not be possible to assemble the source code with native assemblers, which are typically limited to six-character identifiers.
With the exception of the Model 210, Series II and Series III MDS machines have an IOC module with its own 8080 processor which handles the keyboard, CRT display, and integrated single-density floppy controller.
There are at least six released versions of the IOC 8080 firmware:
- original (unenhanced, 8257 DMAC) - part numbers unknown
- original (unenhanced, 8237 DMAC) - part numbers unknown
- enhanced - part numbers 104593-001 through -004
- enhanced - part numbers 104688-001 through -004
- enhanced - part numbers 104692-001 through -004
- IOC-III - uses new version of IOC hardware - part numbers unknown
With the possible exception of the IOC-III, the firmware is supplied as four 2616 or 2716 EPROMs, installed in locations E50 through E53.
The enhanced firmware add improved console support with function key macros and better cursor control, and supports either the 8257 or 8237 DMA controller.
Presently this project has partially reverse-engineered source code for the enhanced IOC, part numbers 104692-00x, in the ioc-enhanced directory.
The IOC has a 2708 (or 2608) EPROM used as the character generator for the CRT. The characters are 6x8 pixels, but some pixels may be shifted a half pixel position to the right, under the control of the two LSBs of the EPROM data.
In the chargen directory there is a Python 3 script "view" which renders the character set in a PDF table.
THe IOC also has an masked-ROM 8041A "UPI" microcontroller which handles the optional printer, paper tape reader, paper tape punch, and UPP (Universal PROM Programmer).
Presently this project has partially reverse-engineered source code for the PIO 8041A, part number 104566-001, in the pio directory.
The pio.asm source code contains conditional assembly directives used by the Makefile to assemble three different versions of pio firmware. The Intel part numbers of the other two versions are unknown, but they were dumped from Series II Model 220 and Model 230 machines. The differences between the versions are fairly minor. The 104566-001 version is believed to be the most recent, and is expected to work properly in any Series II or Series III MDS that uses an IOC module.
The keyboard has an EPROM-based 8741A "UPI" microcontroller which scans the key matrix and provides parallel data to be read by the IOC firmware.
Old Series II MDS keyboards have a repeat key for manual repeat. The enhanced keyboard replaces the repeat key with a function key, and performs auto-repeat.
Presently this project has partially reverse-engineered source code for the unenhanced keyboard 8741A, part number 9100101, in the kbd directory, and for the enhanced keyboard 8741A, part number 104675-001, in the kbd-enhanced directory.
Note that the MDS keyboard uses a "bit-paired" arrangement, as common for ASCII equipment in the 1960s and 1970s (e.g., Teletype model 33), rather than the now-ubiquitous "typewriter-paired" arrangment. This makes use of the MDS keyboard awkward for experienced typists. The key matrix position to character code table in the 8741A could be altered, and different keycaps installed, to obtain a typewriter-paired arrangement.
Copyright is asserted on the reverse-engineered source code, but not on the original binary code provided in ROM, PROM, or EPROM by Intel.
This program is free software: you can redistribute it and/or modify it under the terms of version 3 of the GNU General Public License as published by the Free Software Foundation.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.