Re: VIC-II, CIA, keyboard differences

From: Segher Boessenkool <>
Date: Fri, 9 Dec 2011 23:23:50 +0100
Message-Id: <>
> What would you load to the timer register to emulate a raster  
> interrupt?  I never had a "new" C64. $4cc7 worked for me. It is  
> 312*63-1. On the 6522 VIA (VIC-20), you will have to subtract 2  
> instead of 1.

The same value should work.

The difference here between old and new CIA chips is that the old
chips trigger the timer IRQ a cycle later than the new chips; they
do have the same period for continuous mode though.

> One more interesting trick is distinguishing the left shift from  
> shift lock. The shift lock key should have a lower resistance. If  
> you program one of the connected keyboard matrix lines as an output  
> '1' and another as an output '0', the shift lock will force the '1'  
> output to '0', but the normal left shift key won't.



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Received on 2011-12-09 23:00:04

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