Hi folks, I'm at the point of troubleshooting this 8085 board where I need to test all the RAM.
The code loops at an IN looking for....something. Based on other assembly programs I've looked at the code is very similar to eg a disk controller looking for a READY signal from a drive. Trouble is I have no idea what's expected to be at I/O port 0xE3. If it was one of the peripheral chips I'd expect a chip select line to go low. The 74LS139 that does chip select is OK - I've tested it off-board and all traces going to it buzz out OK. The code uses upper RAM as a scratch pad so what I'd like to do is replace the $0000 ROM with an EPROM containing RAM test code. I've found incomplete examples that need to be tailored so before I go reinventing the wheel has anyone got a working example I can use? Warnings of things I should and shouldn't do? RAM is at $8000-$FFFF, and at least some of it is ok since the stack pointer is up at 0xF0B3 and I can trace the code by watching which addresses it's reading. Cheers! -- Adrian/Witchy Binary Dinosaurs creator/curator Www.binarydinosaurs.co.uk - the UK's biggest private home computer collection?
