Thread: Ortonview PCB
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Old 15th Sep 2021, 9:20 am   #508
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,538
Default Re: Ortonview PCB

Indeed, and although we would originally have used this to reverse the need to multiplex one pin of the 877, we could instead use that extra pin as a video blanking output to hold the video line at black level during the 'bright line' period.

We would need to do this only when the relevant area of the screen (upper/lower) is in normal (not inverse) mode, because in inverse mode the 'inactive' area of the screen - the wide border surrounding the active area - is white anyway, so the bright line will blend into it.

The code should work as-is in an 887, although it may require some jiggling of the configuration bits to make sure any extra features of the 887 are turned off. A useful first check would be to see if using an 887 breaks the graphics mode in the same way as the 877A does.

Incidentally if we went to the PLCC version of the chips concerned, that would make extra I/O pins available on any of them. Although such packages are hopeless for hobbyist / stripboard use, it's not too difficult to solder a PLCC package directly to a PCB.
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