magore@watdcsu.UUCP (M.A.Gore - ICR) (07/29/86)
I have been experimenting with the ATARI 520ST in EXTERNAL SYNC mode
and I am looking for some help. This is not well documented. I will
post a summary of E-mail replies (if I get any). Anyone at ATARI listinging???
Here is what I have done:
Set $ff820a to $fd from $fc and drive HSYNC pin 9 and VSYNC pin12
via 470 ohm resisters from an external source. The video information does
NOT seem to follow HSYNC input *exactly* but rather seems drift for about
a byte then re-sync !!!!
Very odd.
See diagram below.
VSYNC ================================
H |.
S | . <= Video boarder
Y | .
N | . <= drifting away from the horizontal boarder!!!
C |. <= after about 8 pixels it instantly reverts to the
| . <= boarder again !!!
| .
| . <= slope is a function of drift from NTSC norm.
|.
| .
etc.
The camera is NOT running HSYNC *exactly* at the same HSYNC that
the ATARI would if it were providing syncs. Should not this slack
be taken up in the blanking area? Of course I know little about the
chip as it is....What should I do with *BLANK and DE on the GLUE chip
are they converted to inputs also ????
I am making a sampling digitizer that uses the ATARI for
timing with respect to the syncs. Any help would be MOST welcome.
Mike Gore Institute of Computer Research.