Commodore 64 diagnostic cartridges, this needs a diagnostic test harness to fully test the machine. The original has been reverse engineered by Ray Carlsen with various pictures here, and also on zimmers.
Dave Stevenson, which allowed the 2532 to be programmed with my EPROM programmer set to 2732.
Stack IEEE-488 cart I tested previously. I've reverse engineered the design and then simplified it (and reduced the chip count) by using 75150 and 75151 buffers. There is also 32K RAM under the ROM chip and provision for a diode in the IRQ line of the 6522 should that prove necessary for WDC chips.
PET microSD into a single cartridge, 'the Penultimate Cartridge'. That's going to be quite a challenge, so I am testing out all the elements separately first.
Anders from Sweden has uploaded a video demonstrating VIC20 diagnostics using one of my VIC20 ROM/RAM Cartridges.
ROM/RAM cartridge is now finished (and that went on to become the Penultimate Cartridge).
Diagnostic boards and loopback cable are available from my Tindie store, either as PCBs, kits of parts, or assembled and tested sets.