Re: NTSC VIC-II timing

Date: Wed, 21 Jun 2017 21:15:56 +0200
Message-ID: <3722974.ff5yK6GTiG@rakete>
On Wednesday 21 June 2017, 14:08:43 Segher Boessenkool 
<> wrote:
> On Wed, Jun 21, 2017 at 06:46:08PM +0100, smf wrote:
> > On 21/06/2017 18:29, wrote:
> > >... that I never used LP IRQs but thought that it would trigger only
> > >when the button line is grounded within a specific timing window so
> > >some kind of synchronisation with raster position would be required
> > >for the IRQ to happen. But that's a different subject anyway.
> > 
> > A light pen is a simple sensor that triggers when a brighter than normal
> > light is detected. The VIC just latches the x & y position & fires an
> > IRQ when it is triggered, because it assumes that if the light pen can
> > see the gun then it must be over the current pixel.
> > 
> > Adding something to VIC to ignore pulses outside the visible portion of
> > the display would be a waste of space.
> IIRC the LP stuff can be triggered only once per frame, this makes it
> a bit inconvenient to use for non-lightpen uses like we are discussing
> here.  It would be nice if we could just read out the current X coor
> directly, but nope.

wasnt that also different between VIC revisions.... older one will trigger 
only once per frame, newer can do it any time again? like with sprite 


Man kann auch saufen statt rumweinen. Hilft gleichzeitig der Wirtschaft und 
dem Staat! 

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Received on 2017-06-21 20:02:23

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