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Old 17th Sep 2020, 11:20 pm   #50
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 8,630
Default Re: I found it !. A very sorry looking MK14

The hex code for NOP in SC/MP is 0x08, so in theory you can make something which will apply that hex code to the data bus all the time or just during _NRDS and the CPU should just sweep majestically through the address range executing all the NOPs.

You'd need to remove anything else which might try to place data on the bus in response to a read from any part of the address range - RAMs, PROM, etc.

If you make a breakout adaptor from a standard EPROM or EEPROM pinout to 2 * 16 pin headers to plug into the PROM sockets you can try writing little bits of test code to exercise various parts of the circuit to see if they behave as expected.

Like this: I have this one programmed with the 'Old' OS and 'New' OS, selectable, so I can run tests with either OS. I used ordinary 16-pin IC sockets as the 16-pin 'header plugs' which plug into the PROM sockets.

Edit: Cross posted with Mark.
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