I've been trying to get the emulated 88-VI RTC board working in my Altair Clone, and I've been using the instructions in the provided MITS manual. However, I can't seem to find any information about how to actually set it to use the 60 Hz line frequency and change the divider. The example code tells me to strap it with a 60 Hz / 1 rate, but all I can find is a table that describes them, not information about which address controls this. It makes me yearn for my lovely Atmel datasheets.
As I understand it, the process is to have a JMP to an interrupt service routine at 070q, which should jump into the address of START: in the program they provide. The interrupt cycle in the 8080 will interrupt my normal program, push the PC onto the stack, fetch an opcode at 070q, JMP to START:, and hit a RET and pop the PC out. Is that right? The time itself will be updated every interrupt cycle and stored at 0x1FF4 - 0x1FF7.
Now, this 070q is determined by which RST instruction the 88-VI board picks, right? In the admin configuration menu it says I'm using int. vector 1 for my RTC board. Is it looking at some other address?
I think the only thing I'm missing is getting the interrupt to actually happen. I'm calling the provided INIT: manually, which puts 0xF0 out on 0xFE to initialize the RTC, then enables interrupts and returns.