But if we design a complete new Plus1 with a cpld for decoding and SWR bank switching I think there is plenty of room on the board to add a 6522 VIA and the connector for the CH375B board. There is also room for SW-RAM (e.g. a 128KB chip) and the Plus1 ROM and DFS for the CH375B (in one EEPROM).
When this board has so much room for additional SWRoms, it won't hurt to sacrifice one cartridge slot and we can create a new one with one or two connectors for the Tube and a BBC compatible user port. Maybe we can also work out a 1 MHz bus connector as well. This will certainly fit if the dust cover around the cartridge slots is removed.
The most important chips on the board will be:
- EEPROM for Plus1 ROM and DFS
- 128KB RAM for SW-Ram (non-battery backup but with write protection
- ADC0844 (still available on Ebay and Farnell)
- 74LS273 for printer port
- 6522 for user port
- CPLD for decoding logic, maybe with a 74LS30 to save a couple of input lines.
If you have a Plus1 then you can simply exchange the boards without destroying the housing. If you don't have a Plus1, you'll have one without housing.
Any thoughts about this project?