Commodore LCD Firmware, Schematics, and Specifications

• Posted by Mike Naberezny in Hardware

  Download images of the EPROMs in Bil Herd’s Commodore LCD prototype:
  commodore-lcd-roms-bil-herd.zip (Added Oct 4, 2008)

  Download images of the EPROMs in Jeff Porter’s Commodore LCD prototype:
  commodore-lcd-roms-jeff-porter.zip (Added May 24, 2023)

  Download the prelim spec: commodore-lcd-preliminary-spec.pdf (Added May 15, 2012)
  Download more specifications: commodore-lcd-specs.zip (Added Mar 11, 2017)
  Download the schematics: commodore-lcd-schematics.zip (Added May 27, 2022)
  

  I’ve always been curious about this machine so I sent my EPROM programmer to Bil so that he could read the EPROMs. Bil was very kind to do this and we should all thank him for it. This is the first time that these images have been seen in many years.

  Start your disassemblers!

  Update May 15, 2012: Via Bil Herd, Bob Russell has provided the Preliminary Specification of the LCD. The actual prototype hardware owned by Bil Herd has quite a few differences from this spec.

  Update Jan 21, 2014: Gábor Lénárt used these dumps to create a Commodore LCD emulator in JavaScript. Incredible work!

  Update Nov 28, 2014: Bil Herd has posted a Commodore LCD Teardown video on YouTube.

  Update Dec 7, 2016: Added a dump of the character ROM from Bil’s LCD and photos. The character ROM is socket U16, which appears to be a 2332 pinout like the C64. The character ROM itself is a 2764 EPROM with a sticker “LCD CHAR ROM“. The extra pins hang out of the socket and are tied to Vcc with hand-wiring, including the highest address line, so 4K is readable by the LCD. Bil and I dumped this 2764 in my EPROM programmer. We did not disturb the hand-wiring, so we only read 4K of it (like the LCD does). The data layout is like other Commodore character ROMs. Steve Gray created a rendering of it. The character set is interesting compared to other Commodore computers; e.g. the presence of a tilde and curly braces that were perhaps added to support the built-in terminal.

  Update Mar 11, 2017: Added a new ZIP file, commodore-lcd-specs.zip, with specifications. It includes detailed technical descriptions of the LCD controller and MMU chips. These were scanned by Andy Finkel and forwarded by Bil Herd.

  Update May 12, 2022: I’ve created a GitHub repository with Commodore LCD ROM disassemblies. I started with the LCD KERNAL disassembly by Gábor Lénárt and have disassembled and commented more routines.

  Update May 27, 2022: Added a new ZIP file, commodore-lcd-schematics.zip, with the schematics. The original pages are owned by Bil Herd. Thanks to Bil for allowing them to be scanned and posted.

  Update June 1, 2022: Johan Grip has redrawn the schematics in KiCad and released his files under the CERN Open Hardware License v2.0 Strongly-Reciprocal (CERN-OHL-S). According to this explanation, it is a “strong copyleft” license. Alternatively, the original Commodore LCD schematics are available and contain the same information.

  Update May 24, 2023: Added a new ZIP file, commodore-lcd-roms-jeff-porter.zip, with dumps of the EPROM’s from Jeff Porter’s Commodore CLD prototype. Photos of Jeff’s CLCD and his printer are also available.