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TSU Meeting MONDAY — April 1, 2024

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David, Eduardo, Adam Trionfo, Carl Miles, Gustavo, Ricardo Calcagno, Paul Holmgren, Tim Swenson, Ryan Gray, Jeff K., Rich, Joe

Eduardo (Argentina) walked the group through a new CP/M board he's designing for the TS2068. It uses port 7 to bank-switch eight 128K RAM pages plus a 32K EEPROM that replaces the original ROM and holds a boot loader targeted at the Larken, JLO, and AERCO disk systems, with a 64K all-RAM mode whose video memory is protected from peripheral access via the ROMCS signal. He's looking for collaborators. Ricardo Calcagno offered to extend the TS-Pico for the project: the Pico can be put into pure I/O mode and serve sector-level reads/writes from virtual disk images, which would give the board CP/M storage without needing real floppies. Eduardo also floated using the TS-2050 modem on interrupts from the bioROM.

David demonstrated Chromasoft, Bill Russell's early-80s pseudo-color program for the ZX81/TS1000, recovered from a cassette Paul Holmgren had sent in. It loaded on the first try into the EightyOne emulator; the program flashes black-and-white frames fast enough to fool the eye into perceiving color, originally intended to be viewed through a colored gel overlay (probably amber). Results over Zoom playback varied — some saw faint reds and blues, others nothing — and the consensus was that a real CRT's phosphor persistence is what makes the trick work. The code is three REM lines of Z80, hidden behind a listing that starts at line 3.

Carl Miles reported continued small-batch production of the 1510 cartridge clone and progress on his ZX80 clone: video came up cleanly after dropping the shift-register clock resistor and adding a trim pot, with an RGB SCART-to-HDMI path via a Sega Genesis 2 adapter still to wire up. He also showed the 3D-printed Pico cases (filament, top piece warped). Ryan Gray walked through his P-file → 1510 ROM cartridge converter: the simple AROS-style loader works on the original four programs but fails on real software that does CRC checks over the system variables (e.g. ViewCalc, ViewFile), stashes machine code in the variables area, or sets auto-start addresses outside the program. Some converted ROMs run in EightyOne's ZX81 mode but crash in TS1500 mode, which the group suspects is an emulator bug; HotZ in particular collides with the second cartridge ROM and may need a RAM-bearing cartridge.

Tim Swenson surfaced more finds from Bill Miller's collection — a TS-Count accounting manual (author Jim Payne may join a future meeting) and the A&J Micro Drive 2000 ROM source listing. Gustavo confirmed A&J used the same tape-routine rewriting trick as the TS-Pico, settling an open question about whether A&J and Timex coordinated on the Microdrive (they did not); Carl will dump the A&J 2000 EEPROM so the 8080-mnemonic Avocet source can be cross-checked. Joe is reverse-engineering a modified TS2068 board (custom ROM, white-on-black boot) that the startup initials "W.J." identified as Willie Jones's work. Tim also published a documentation/tutorial for Andy Ray's ZX-Beta tracker (needs a Zonics or ZX-Spectrum AY chip) and set a September 1 deadline for newsletter submissions. Next meeting is Sunday April 21 at 2 pm Eastern.

Highlights

  • Eduardo unveiled a TS2068 CP/M board (port-7 bank switching, 64K paged RAM, EEPROM boot ROM for Larken/JLO/AERCO); Ricardo offered TS-Pico integration as the storage backend.
  • Chromasoft, Bill Russell's flickering pseudo-color ZX81 program, was recovered from a Paul Holmgren cassette and ran first-try in EightyOne.
  • Ryan's P-file → 1510 ROM converter is exposing copy-protection tricks (system-variable CRCs, machine code in the variables area, off-program auto-start addresses).
  • Carl got his ZX80 clone displaying video by dropping the shift-register clock resistor and adding a trim pot; SCART-to-HDMI path next.
  • Bill Miller-collection finds: TS-Count manual (author Jim Payne may join), and the A&J Micro Drive 2000 ROM source — confirming A&J independently used the same tape-routine rewrite trick as the Pico.

Projects discussed: TS1510 Cartridge Interface Clone · TS-Pico · The Bill Miller Collection Topics: CP/M · TS1510 cartridge interface · Cartridges, EPROM & dumping · TS1000 / ZX81 / TS1500 · Tape & library archiving (TAP/TZX) · Machine code, Z80 & assemblers

Summary generated from the meeting recording; the full transcript is kept in the group's private archive.