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VDC timings

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oziphantom C-64 User Posts: 198	VDC timings Nov 16, 2018 6:24:31 GMT Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by oziphantom on Nov 16, 2018 6:24:31 GMT Has anybody worked out how many cycles the VDC uses "per frame" and "per line", in 1mhz CIA terms? Or maybe we can fine tune the number of lines to get it to sync with the VIC frame rate so we can use its IRQ to time things?

willymanilly
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Posts: 219

VDC timings Nov 17, 2018 9:07:19 GMT

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Post by willymanilly on Nov 17, 2018 9:07:19 GMT

As far as I'm aware the all VDC's have a dot clock of 16Mhz meaning 2000000 VDC cycles per 98524(PAL) or 1022727 (NTSC) VIC cycles.

The following results I posted on the research I'm doing to understand the in depth undocumented VDC behaviour might be of interest to you. I plan on including the VDC cycles per frame/ VIC cycles per frame ratio in my VDC split program when I return home form my holiday late next week.

c-128.freeforums.net/thread/600/vdc-raster-split
c-128.freeforums.net/thread/35/8x1-vdc-mode-trick
c-128.freeforums.net/thread/608/vdc-horizontal-display-greater-82

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