Timex Sinclair User Group Meeting — October 3, 2022

David, Adam Trionfo, Paul Anderson, Tim Swenson, Ryan Gray, Carl Miles, Jeff Burrell, Willie, Andy, Keith, Greg

Tim opened with a fresh-off-the-bench Arduino shield that drives the ZX Printer and TS2040 from a microcontroller — a one-resistor board with a ZX81/TS2068-style edge connector and a 9V barrel jack for the ZX Printer. Code is already on GitHub; he'll tidy the silkscreen, publish the Gerbers, and put the design up as a public PCB so anyone can order copies directly. The eventual goal is end-to-end Windows-to-2040 printing, with a Timex/Sinclair 5x7 font instead of the placeholder font he demoed.

Ryan walked through his QuickFont editor (reserves 768 bytes of RAM via CLEAR, points the font system variable at it, lets you edit each glyph and save the result as a code block). He's just made it work under the OS-64 ROM as well — the ROM font lives at a different address there and the 512-pixel high-res mode draws text on a 256-pixel grid, so plotting was right but text landed off-centre until he chased down the pointers. That led into a long aside on the 2068's odd 14.112 MHz crystal not being a clean multiple of the color burst, and the fringing you get with green-paper/violet-ink combinations.

The bulk of the meeting was cartridges. Willie's new BackBit 2068 adapter (from Evie) was failing to load anything; David explained the standard .dck/dock-file format is the Werevo cartridge dump with a nine-byte header, and you need to strip those nine bytes (hex editor, sublime text, tail -c, HxD on Windows) before burning to EPROM or feeding to the BackBit. Adam is disassembling the Qbert prototype LROS cartridge with DZ80, trying to find I/O port reads for the joystick — Jeff suggested grepping the binary for IN/OUT opcode pairs since the game may simply not support joysticks. That spun off a clear explanation of LROS (replaces the Timex ROM, runs from $0000, must reimplement keyboard/video) vs AROS (lives at $8000+ and uses the Timex ROM routines), and how the Portuguese TC2068 Spectrum cartridge / Bob Orfeld's patched Spectrum ROM both effectively act as LROSes. Keith described how the AERCO disk interface initialises as an LROS, copies itself into the second chunk, patches the J-error vector, and gives you 64K (his has 256K) of dock-bank RAM to work in, and how he modified it to run Spectrum ROM and OS-64 code as well.

Closing items: Adam asked how to author a BASIC-program AROS cartridge — David recalled the Tom Woods / Bob Orfeld / Bill Jones work (set the basic-start system variable so the program loads at chunk 4 + 8-byte header, then dump tokenised BASIC). Tim Burrell offered to teach Z-Mac's BASIC tokeniser to spit out the right binary format, and Carl took the homework to write up the full recipe. Andy raised the MIDI lines wired into the 2068 joystick ports per the schematic (probably for an unreleased Timex MIDI box); David will dig out the diagram and post it to the list. Next meeting set for Sunday October 16 at 2pm Eastern.

Highlights

Tim demoed a working Arduino shield that prints to the ZX Printer / TS2040; Gerbers and public PCB to follow
Ryan got QuickFont running under the OS-64 ROM after chasing the relocated font pointer and 256-pixel text grid
Walkthrough of the dock-file 9-byte header and how to strip it for BackBit / EPROM use
Adam is disassembling the Qbert prototype LROS cartridge with DZ80, hunting for joystick I/O
Homework for next meeting (Oct 16): a documented recipe for building a BASIC-program AROS cartridge, with Z-Mac generating the tokenised binary

Topics: Cartridges, EPROM & dumping · Machine code, Z80 & assemblers · Printers & plotters · BASIC programming · Pico / modern interfaces (UnoDos, etc.) · Disk & floppy systems (Larken, AERCO, Oliger)

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