Atari Beaglebone Expansion
- Write $LL to $D7HH to request page $HHLL.
- Wait for ~700 CPU cycles for page to be loaded.
- Make sure 6502 program counter and ANTIC stay out of page range during loading.
- Page will appear to be filled with $FF during load.
- Upon load completion, 24K page will visible from $4000 through $9fff.
- Beaglebone
- Jumper Wire
- Jumper Wire
- Jumper Wire
- Five 8-bit level shifters
- 60 pin edge connector (cut down to 50 pins)
- Spare 34 pin ATA ribbon cable
- Spare 15 pin serial ribbon cable
I've only tested on a stock NTSC Atari 600XL. ABX does assert EXTSEL on reads from the page range, but I haven't verified that main memory is properly disabled during these reads. If not, there would be bus contention on a system with more than 16K RAM. Importantly, ABX does not yet keep track of the state of PORTB or heed EXTENB, so it does cause bus contention when the self-test ROM is enabled.