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IanBland · 14th Sep 2019, 11:49 pm

Thanks for the answer! What's puzzling me (I'm an absolute n00b compared to everyone else on this forum regarding video signals) is how you get that from a crystal at 14.75 MHz, as I understand 625 line TV is 6.5MHz and that's not a simple ratio. Would you be kind enough to give a simple explanation?

(I'm interested partly because it's a cool project and partly because for reasons unknown I've found myself contemplating Sinclair micros again and the ZX81's "novel" approach to getting video without a video chip, and in that the Z80 had to run at 3.25MHz (slowing it even further from its possible 4MHz) to sync with the video).

14th Sep 2019, 11:49 pm	#7
IanBland Hexode Join Date: May 2015 Location: Northampton, Northants, UK. Posts: 380	Re: Orton PIC video clock Thanks for the answer! What's puzzling me (I'm an absolute n00b compared to everyone else on this forum regarding video signals) is how you get that from a crystal at 14.75 MHz, as I understand 625 line TV is 6.5MHz and that's not a simple ratio. Would you be kind enough to give a simple explanation? (I'm interested partly because it's a cool project and partly because for reasons unknown I've found myself contemplating Sinclair micros again and the ZX81's "novel" approach to getting video without a video chip, and in that the Z80 had to run at 3.25MHz (slowing it even further from its possible 4MHz) to sync with the video).