Re: NTSC VIC-II timing

Date: Wed, 21 Jun 2017 19:29:06 +0200
Message-Id: <>
> On 2017-06-21, at 19:17, Gerrit Heitsch <> wrote:
>>> Excellent fun!  It sees if the light pen interrupt can be triggered
>>> between raster lines x'136 and 2; if so, it's a 6569R1, if not, not.
>> That's very interesting too! How does one trigger LP IRQ from within software alone? Is it a kind of raster position / CIA port combination?
> Well, the LP Input is connected to the joystick ports and shares a Pin with PB4 of the CIA on U1.

Hardware side sure. What I meant was...

> So you can trigger LP IRQs via software.

... 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.

SD! -

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Received on 2017-06-21 18:03:36

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