I've just seen the video, and this is definitely a great idea. If I understand correctly, the working principle is that the rotary encoder sets the higher bits of the eeprom's address pins.
The "classic" RC2014 (the original model with 32KB RAM and 8KB ROM, not the new fancy ones with 512+KB that run CP/M) uses something like that with jumpers (it has a 64KB EEPROM and 3 jumpers allowing to choose 1 of 8 ROM images). I didn't like having to mess with jumpers everytime I wanted to switch ROM, so a couple of years ago I made a small PCB to replace them with an Attiny13A (the cheapest available MC with enough pins at the time). I wonder if something like that could be implemented on top of the Dial-A-ROM because this is incredibly convenient to use on the RC2014. Basically, the Attiny selects the ROM by setting the higher bits of address of the EEPROM. It also monitors the reset signal, and whenever it's low for more than 2 seconds it selects the next ROM image (it keeps switching image every 2 seconds while RESET is low) and when you release the RESET button, it saves the newly selected ROM number in its internal EEPROM for the next cold boot). Here is a picture (this is the green PCB) : http://pics.lefauve.org/PXL_20230226_224656582.jpg The 3 LED show the currently selected ROM number. They're always on but I think that if we connect their cathode to RESET instead of GND, they will just light up while the RESET button is pressed so it shouldn't have too much impact on the battery life. The one jumper on the PCB is just here to force A15 to Vcc, which is convenient for me because I'm using a 32KB EEPROM at the moment; that shouldn't be needed with the M100. The main issue I can see is that it would still require removing the trapdoor to see the leds when switching ROM image, which kind of defeats the "instant option ROM switch by the press of a button" but perhaps one of you guys will come with a solution for this? ;o) Cheers, Eric
