External 3B1 Monitor Project Status; and help needed
Thad P Floryan
thad at cup.portal.com
Wed Jan 30 23:23:18 AEST 1991
Welllll, most aspects of the External Monitor Project are working well, esp.
after inverting the vertical sync signal.
Only real problem remaining seems to be due to the 3B1 not quite producing a
"Hercules" compatible video signal ... my guess is the onset of the video
information seems to be too soon after a horizontal sync, causing the first
several pixels on each line to not be displayed.
Attempts to delay the video by running through a l-o-n-g chain of inverters
doesn't do anything discernibly different and I'm wondering if a digital delay
line might be necessary.
If anyone has experience with "digital" video (contrasted with "analog" video)
or can point me to some reference books that might address this kind of
problem, I'd be greatly appreciative.
It also seems that "Hercules"-compatible monitors don't have any horizontal
width adjustments meaning the 3B1's display doesn't span the entire CRT.
Several different monitors I've checked also have only the same four internal
potentiometer adjustments the BTC monitor has (besides the "external" bright
and contrast controls):
Contrast that with the complete array of adjustments available with the stock
3B1 monitor. Sigh.
And it appears the Hercules monitors automatically center the image on the CRT
face, so it would appear that some method of "stretching" the horizontal scan
is needed (to fill the CRT left-to-right). Again, any ideas or pointers to
reference material would be appreciated.
Please post any replies since email to/from "here" is unreliable and because
my email address will likely be changing within the next day.
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