Is there an explanation in the docs (apologies if I've overlooked it) on when these pins cannot be used because the VM relies on these jumpers:
PD2/INT0 is jumpered to PC6/TOSC1
PD3/INT1 is jumpered to PC1/SDA
PD6/ICP is jumpered to PC0/SCL
PB1/T1 is jumpered to PC7/TOSC2
PB2/AIN0 is jumpered to PA2/ADC2
In particular, I'd like to use INT0 and INT1 and I'm not sure if the VM uses these for something or when some user program function call is done such as software UARTs.
reserved I/O pins for VM?
The VM doesn't rely on the pins being connected and there is no requirement for them to be connected. It's just that on a 24-pin package there were no pins left to bring out the additional functionality. ZX-40 and ZX-44 users can use INT0 independently of Port C Bit 6 but a ZX-24 user must give up Port C Bit 6 functionality in order to use INT0. The same applies to the other pins mentioned.
- Don Kinzer