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.