PAL video VSYNC timing

I am putting together an 8-bit CPU-based computer which is to have a colour video display. In my research on PAL video timings, I notice that the vertical sync is a series of pulses. If I am just using a non- interlace display, do I strictly need to have a series of pulses?

I have made a TV-based video display in the past and just used a 192uS pulse every 20ms as VSYNC. This seemed to work ok but I am wondering if it's actually important to have the series of long and short VSYNC pulses.

Reply to
bonzer
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This series of pulses are called serration pulses in the NTSC world. They are meant to keep the horizontal oscillator locked during the lengthy vertical retrace. Since TVs don't use analog circuits anymore for sync, the pulses are not strictly necessary. If you low-pass filter this waveform enough, you end up with a VSYNC without the pulses.

You will note that the serration pulses are at 2H, so that the interlaced display doesn't affect the lock of the H oscillator.

Judging by the amount of 10 year old TVs I see in the garbage every week, I think the amount of TVs older than 10 years is negligeable.

Modern TVs are very robust when it comes to digesting video signals. They lock on to anything and scan double for you. (In the case of the LCD TVs I see all over the place).

Anyways, sounds like you are doing a fun project.

Reply to
a7yvm109gf5d1

I suggest asking comp.sys.sinclair The old guys over there are still obsessed with the inner workings of 1980's home computers that use TV's as displays.

Bob

Reply to
Bob

On a sunny day (Mon, 08 Oct 2007 14:26:18 -0700) it happened bonzer wrote in :

No.

Only if interlace. Just xor H and V.

Reply to
Jan Panteltje

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