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Old 13 February 2014, 20:13   #25
mark_k
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Quote:
Originally Posted by Toni Wilen View Post
EDIT: it also says vertical is "half-rate" only in interlace, non-lace is normal, both PAL and NTSC.
I don't think it does say that necessarily. My reading of it is that the vertical reset pulses provided by the genlock are always at half-rate (page XII-29). Or perhaps the text on that page was written assuming that the external video source is spec-compliant NTSC/PAL (so always interlaced)?

The vertical counter explanation on page XII-28 (in interlace mode vs in non-interlace mode) is I think referring to the Amiga display mode rather than the external video source connected to the genlock. But it isn't completely clear to me:
"In non-interlace mode the vertical counter is set to operate with either long or short fields, depending on the last value that the software wrote to the FRAME bit. In this mode, whenever an external VSY* pulse is applied, the counter is reset to line count 000 (first line) at the beginning of the next horizontal line."

I assume the FRAME bit means the LOF bit in VPOSR/W. Could that be taken to mean, with half-rate vertical pulses, for a field with no VSY* pulse the vertical counter rolls over to 0 after counting to the appropriate value depending on the LOF bit. And when there is a VSY* pulse the vertical counter resets to zero???

This needs testing on real hardware.
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