Atari 8bit Assembler in Atari 5200 / 8-bit Programming Posted 2 hours ago · Edited 2 hours ago by danwinslow For the TSR type thing, you have to drive it off of an interrupt. VBI/VBD is always an option, you can chain yourself in there even if something else is already (provided they did it the right way). I've also driven things off of one of the pokey timers. As always, you need to attend to the stack/regs and CRITIC and so forth. Anyways, from a high level: get yourself loaded somewhere safe, steal the interrupt vector by replacing it with your routine, saving off the old one if you want to chain to it when you are done (VBI/VBD, usually pokey you wouldn't do that) and also to replace it if you quit. You finish the VBI/VBD by jumping through the old vector, if I recall, and from pokey you'd RTI. Both need attention to putting the stack and regs back together as necessary. For pokey you need to do some setup and control the rate you want. There's lots of examples in docs about VBI/VBD, pokey interrupts are slightly more exotic but there's still a lot out there. If you are ok with cross compiling on a PC, you could look at MADS or CA65. I used CA65, but if you write the C correctly you can actually use CC65 to do interrupts fairly well. The whole CC65 toolchain is fairly complicated, so you might want to look at MADS for just straight assembly. If you want to do it natively on the Atari, I'm not sure what's best but I'm sure someone will have a recommendation. For the BASIC question, I think you just PEEK(addr)+PEEK(addr+1)*256, or use DPEEK(addr) from one of the more advanced BASICs.