Icky wrote: ↑Thu Nov 29, 2018 9:54 pm
Exxos is awesome - How did you do that
I lifted that highlighted pin which, and linked to small wire from it to the BLANKing line...
So when BLANK is high, it selects D-RGB mode, when BLANK is low it selects A-RGB mode...
Technically the A-RGB lines are floating, but at this time of night I did not care, and it works anyway so
Brilliant so it was blanking related
Question now is to compare original circuit against new DAC circuit to see improvement.
Re: Video driver thoughts
Posted: Thu Nov 29, 2018 10:06 pm
by exxos
Icky wrote: ↑Thu Nov 29, 2018 10:00 pm
Question now is to compare original circuit against new DAC circuit to see improvement.
Sadly it looks the same
Mostly I was trying to get rid of the vertical noise lines in the drag bar but they are still there... Only now they seem to be flickering a little bit...
I do have some 40R resistors in series with the RGB outputs with 47pF on them.. so its not like its noise there...
Gave myself permission to upload a high res shot to illustrate this...
IMG_3626.JPG (4.91 MiB) Viewed 6104 times
The thing is, I don't think I saw this on the Falcon video.. and its the same chip now
BTW - the jumper does up the brightness a little, not a great deal...
Re: Video driver thoughts
Posted: Thu Nov 29, 2018 10:08 pm
by stephen_usher
So, is this a similar issue to the “front porch”/“back porch” video generation issues that the early ZX81 ULAs had?
Basically in that case the ULA didn’t produce a “back porch” on the video signal so the TV/monitor circuitry couldn’t determine the base level of the signal. In the case of the ZX81 color TVs took the “white” level to be black and dimmed the display accordingly.
I guess that in this case the monitor could be taking a floating value as the black level, when the border is white. When it’s black then it emulates a back porch.
Re: Video driver thoughts
Posted: Thu Nov 29, 2018 10:09 pm
by PhilC
Well done guys. Looking better and better.
You'll get there with the quality thing Exxos, just take a bit of tweaking is all.
Will lift the pin tomorrow and catch up yet again, lol.
Still didn't fix the floppy drive problem, too busy with Fallout 76.
Icky wrote: ↑Thu Nov 29, 2018 10:00 pm
Question now is to compare original circuit against new DAC circuit to see improvement.
Sadly it looks the same
Mostly I was trying to get rid of the vertical noise lines in the drag bar but they are still there... Only now they seem to be flickering a little bit...
I do have some 40R resistors in series with the RGB outputs with 47pF on them.. so its not like its noise there...
Gave myself permission to upload a high res shot to illustrate this...
IMG_3626.JPG
The thing is, I don't think I saw this on the Falcon video.. and its the same chip now
BTW - the jumper does up the brightness a little, not a great deal...
It looks like your display is doing a great deal of “sharpening”. Lots of nasty halos!