Look up March C. It is one of the most simple but thorough RAM test. It is the test most commonly used by manufactures. It only needs one address counter and unlike other is fast. The coding is simple. Dwight ________________________________ From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Adrian Graham <witchy at binarydinosaurs.co.uk> Sent: Monday, February 13, 2017 3:03 AM To: Discussion: On-Topic and Off-Topic Posts Subject: 8085 RAM testing program 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?