8085 RAM testing program

dwight dkelvey at hotmail.com
Mon Feb 13 08:18:37 CST 2017

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.


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


Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer

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