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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 10th Jul 2024, 12:28 am   #1
Buzby123's Avatar
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
Posts: 690
Default NOP generators, different to what I expected.

Browsing round the web, I found these NOP generators ...

These devices are stand-alone devices to test CPU chips by forcing them to execute NOPs, and then viewing LEDs on the address bus as a quick check that the CPU is working.

These are totally different to what I have always known a NOP generator to be.

My understanding, and the ones I built back in the day, was a device that replaced the target CPU in a system, and swept through its address space by executing NOPS. By forcing the RD/WR strobes on every NOP you could do a rough check that all the address decoding was working properly.

So, if somebody said 'I've got a NOP generator', what would you think they had ?


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Old 10th Jul 2024, 12:59 am   #2
Join Date: Mar 2011
Location: North Yorkshire, UK.
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Default Re: NOP generators, different to what I expected.

Hi Buzby
I think its the same thing but one way forces the existing processor in situ to do NOPs, and the other is a plug-in unit probably with the very same processor on a daughterboard, again forced to run NOPs.
I've also seen devices which were just a binary counter feeding the address lines, that could be free-run or single stepped - but thats not a NOP generator, more an 'address sequencer'
Either way I've never used one or felt the need for one
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Old 10th Jul 2024, 10:10 am   #3
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Default Re: NOP generators, different to what I expected.

They are a pretty much essential first line of attack for working on things like PETs - some of the PET cases we have worked through here would have been much more difficult without having a NOP generator handy to exercise all of the address lines and therefore also the chip select lines, to check that they are all working.
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Old 10th Jul 2024, 11:27 am   #4
Join Date: May 2012
Location: Perth, Scotland
Posts: 1,852
Default Re: NOP generators, different to what I expected.

The NOP generator I cobbled together, and then replaced with the one below was designed to be used in the PET itself, and does not have the ability to actually test the 6502 itself which is what the first post seems to do.

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