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Post by VDC 8x2 on Jun 18, 2014 3:53:35 GMT
How many cycles of code do you think can be run during the vdc vblank?
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Post by hydrophilic on Jun 19, 2014 4:19:04 GMT
As far as I can tell, VBlank as reported by the VDC, lasts from the bottom border until the top border. For NTSC, this is about 262-200 = 62 rasters or for PAL 312-200 = 112 rasters. Which is about 62*65 = 4.030 milliseconds, NTSC or 112*63 = 7.056 milliseconds PAL. At 1MHz speed, this would about 4k or 7k cycles respectively; At 2MHz, this would be about 4k*2-5*62= 7.75k cycles NTSC or 7k*2-5*112= 13.55k cycles PAL. How many CPU instructions you can actually execute of course depends on how many cycles the instructions use.
Of course this is contrary to the real VBlank of broadcast standards which lasts about 7 or 6 rasters for NTSC or PAL. Well I don't think analog broadcast is really a standard anymore in the USA, but I hope you know what I mean. Digital TV doesn't really have VBlank...
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