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SiriusHardware · 27th Oct 2020, 9:55 pm

I'm also running charset again, but I have stripped out everything 'cosmetic' and it now just floods 0F12-0FFE and 0B00-0BFF with 3F, the character code for '?' before looping round continually changing just one character on the screen. Specifically, it writes each successive character code to one location over and over again.

So the character which the program is intentionally modifying many times per second, too fast to see individual characters, is the one held in lower screen address 0B27.

The character which is being occasionally, unintentionally, modified in the upper screen area resides at 0F27. So yes, there is a direct relationship between the address which is intentionally being modified and the address which is unintentionally, and only occasionally being modified.

The range of characters / values which the contents of 0B27 get modified to is relatively small, so far I have seen

Letter 'O' (code=0F)
Underscore (code=1F)
Forward Slash (code=2F)
Much less often, '?' (code = 3F).

So obviously, there is also a relationship between the 'Spurious' characters which are being written to 0F27.

Sometimes it can be a matter of seconds between changes, sometimes minutes.

Next experiment: Move the rolling character to another randomly chosen screen location, 0B31

As you might expect, the location which now changes randomly in the upper screen area is 0F31. The range of 'random' characters has the same small range as before - characters whose codes end in 'F'.

27th Oct 2020, 9:55 pm	#658
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,588	Re: Mk14 vdu I'm also running charset again, but I have stripped out everything 'cosmetic' and it now just floods 0F12-0FFE and 0B00-0BFF with 3F, the character code for '?' before looping round continually changing just one character on the screen. Specifically, it writes each successive character code to one location over and over again. So the character which the program is intentionally modifying many times per second, too fast to see individual characters, is the one held in lower screen address 0B27. The character which is being occasionally, unintentionally, modified in the upper screen area resides at 0F27. So yes, there is a direct relationship between the address which is intentionally being modified and the address which is unintentionally, and only occasionally being modified. The range of characters / values which the contents of 0B27 get modified to is relatively small, so far I have seen Letter 'O' (code=0F) Underscore (code=1F) Forward Slash (code=2F) Much less often, '?' (code = 3F). So obviously, there is also a relationship between the 'Spurious' characters which are being written to 0F27. Sometimes it can be a matter of seconds between changes, sometimes minutes. Next experiment: Move the rolling character to another randomly chosen screen location, 0B31 As you might expect, the location which now changes randomly in the upper screen area is 0F31. The range of 'random' characters has the same small range as before - characters whose codes end in 'F'.