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

Karen O · 25th Oct 2020, 8:46 pm

Mark1960 has a point in post #583.

Were the VDU to assert NENIN part way through a write cycle to screen memory, then that write cycle may be corrupted, resulting in temporary corrupted data in memory. Corrupted data may then show up in the screen display.

When the SC/MP is allowed to resume, the SC/MP will repeat the cycle, complete successfully and restore correct data to memory.

I've tried to think of every trick to get graphics mode working on the same pixel clock as text (as I think that this might stop the juddering).

It is interesting that the juddering is not perfectly random.

If it really does shift or not shift on a frame-by-frame basis then it seems to be aware of the 625 frame rate, which is kinda baffling.

So, the effect of corrupted display data may be an illusion.

25th Oct 2020, 8:46 pm	#590
Karen O Rest in Peace Join Date: Jul 2011 Location: Bridgnorth, Shropshire, UK. Posts: 787	Re: Mk14 vdu Mark1960 has a point in post #583. Were the VDU to assert NENIN part way through a write cycle to screen memory, then that write cycle may be corrupted, resulting in temporary corrupted data in memory. Corrupted data may then show up in the screen display. When the SC/MP is allowed to resume, the SC/MP will repeat the cycle, complete successfully and restore correct data to memory. I've tried to think of every trick to get graphics mode working on the same pixel clock as text (as I think that this might stop the juddering). It is interesting that the juddering is not perfectly random. If it really does shift or not shift on a frame-by-frame basis then it seems to be aware of the 625 frame rate, which is kinda baffling. So, the effect of corrupted display data may be an illusion.