Re: [stella] end of frame??

Subject: Re: [stella] end of frame??
From: Erik Mooney <erik@xxxxxxxxxx>
Date: Wed, 31 Oct 2001 13:25:32 -0500
10/31/2001 12:43:49 PM, Chris Wilkson <ecwilkso@xxxxxxx> wrote:

>If the framerate is "too far" from 60Hz, the screen will roll
>vertically.  Back in the good old days, TVs had a vertical hold
>knob that the user could adjust to correct for this, but I don't
>think you can do it with more modern sets.  Of course, the more
>modern sets may be more forgiving of bad NTSC signals.
>"Old tech is better tech" -Chris

I've long been curious about the electrical mechanics of this.
The book Video Demystified, well, didn't.

When a screen rolls, it means that the video source and TV screen
don't agree on where the beam is vertically -- that is, the TV either
reset the beam when the video source didn't expect it, or didn't
when the source did.  I can understand the principles -- if a video
source indicates vertical sync (by dropping luma to zero) too early,
the TV can't readjust the magnetic field for the beam in time, and if
it does so too late, the TV has already "given up" and recycled the
beam.  But how does a vertical-hold knob figure in?

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