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Author Topic: New owner of an abused enterprise (Read 4604 times)

Offline Zozosoft

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Re: New owner of an abused enterprise
« Reply #15 on: 2014.July.31. 16:28:15 »
Will be the next question: do you have a EPROM programmer?

At most of times if the onboard memory are faulty the original EXOS ROM don't make any life sign. Because it is use a CALL instruction for call the memory testing routine, and if the memory are hardly faulty then the return address are corrupted...
Then I wrote a little test ROM which are don't use any bit of the RAM for the program running. Another problem if the onboard (video) memory are faulty then you can't generate proper screen...
My program wrote bytes to RAM and generate beep sound from the readed bits (low and high sound frq) then you can got some life sign from a machine which are do nothing with the original EXOS ROM.
(This test routine are also included in the EXOS 2.4)

Note: not only faulty RAM chips can make this problem. I found many faulty Z80 CPUs which are make bugs when writing memory. Very interesting these are produced in same factory with close date codes!