Re: NTSC VIC-II timing

From: Gerrit Heitsch <>
Date: Wed, 21 Jun 2017 19:17:59 +0200
Message-ID: <>
On 06/21/2017 07:12 PM, wrote:
>> On 2017-06-21, at 18:43, Gerrit Heitsch <> wrote:
>> Before you do that, check if there are other software detectable differences between the 6567R56A (and older) and the 6567R7 (and newer). Those might be easier to detect.
> As just noticed - there is a difference in the number of scan lines, which might in fact be easier to abuse.

Yes, see if the line counter max values differ between them.

>> I suggest this since it's possible by software if you have a 6569R1 or a later VIC and if later, if it's a 6569 or a 8565.
>> Here's what Segher wrote about it:
>> 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. So you can trigger LP IRQs via software.


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Received on 2017-06-21 18:02:52

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