UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Nascom repair

SiriusHardware · 29th Oct 2017, 10:59 pm

While you're waiting for the chips, can you try writing a bit of code which will wiggle an I/O port pin? As before, use no RAM and confine any variables needed to within the registers.

The test which showed _IOREQ activity apparently in response to your code running IN or OUT instructions was indicative, but not absolutely conclusive. The CPU could just have been running wild and executing randomly 'found' I/O instructions.

If you can exert programmed control over one of the I/O ports, then you can be really sure you are able to run working code.

29th Oct 2017, 10:59 pm	#17
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,586	Re: Nascom repair - Looking for clues please While you're waiting for the chips, can you try writing a bit of code which will wiggle an I/O port pin? As before, use no RAM and confine any variables needed to within the registers. The test which showed _IOREQ activity apparently in response to your code running IN or OUT instructions was indicative, but not absolutely conclusive. The CPU could just have been running wild and executing randomly 'found' I/O instructions. If you can exert programmed control over one of the I/O ports, then you can be really sure you are able to run working code.