8085 RAM testing program

Adrian Graham witchy at binarydinosaurs.co.uk
Mon Feb 13 05:03:38 CST 2017

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


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Www.binarydinosaurs.co.uk - the UK's biggest private home computer

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