chysn wrote:If the MINIMON cartridge is plugged in, and then a SmartRAM cartridge is plugged into the MINIMON cartridge, will the VIC-20 see the RAM at $9800 or the MINIMON ROM?
See here:
When the sliding switch SW1 - that one between the reset button and the two jumpers - points towards the VIC-20, then MINIMON (or whatever else is installed in the ZIF socket) is visible in $9800..$9FFF. When SW1 points towards the slave cartridge, whatever the slave cartridge has in I/Ox will be visible for the VIC-20. In the latter case, the I/Ox select signals are pass-through.
The hardware has been crafted judiciously, so SW1 can be changed while the VIC-20 is switched on! Furthermore, those high speed select signals do not go over mechanical contacts, rather the two logic chips in the lower half of the PCB guarantee the integrity of the signals.
Granted, you need to have a good idea when a slave cartridge might need access to its own registers, but you can always position SW1 as necessary: for example, with Mega-Cart as slave cartridge, you would have SW1 point towards MC at power-on or MC reset, so the menu can access the MC hardware registers and NV-RAM in I/Ox, but you can switch SW1 to MINIMON as soon as you leave the Mega-Cart menu and are in the BASIC start-up screen.