VIC-II, CIA, keyboard differences

From: Marko Mäkelä <>
Date: Fri, 9 Dec 2011 11:44:24 +0200
Message-ID: <20111209094424.GB2989@x60s>
Interesting, I did not know that there is a difference in CIA timers 
until it was mentioned here this year.

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.

On Fri, Dec 09, 2011 at 03:18:37AM +0100, Segher Boessenkool wrote:
>>Demos written for the 6569R3 or higher look quite odd on the R1.
>Because of the luminance palette difference, I take it?  Or is there 
>some more awesome difference :-)

On my oldest C64 (with 350ns ceramic DRAM chips), sprites flicker. I 
never tried to troubleshoot it whether it is because of the 6569R1, the 
slow DRAM, or the motherboard. The computer does have some physical 
damage, such as missing keys with the "stick" broken. I got it from 
someone who lived in Spain for a while and had picked the machine up 
from a flea market in the early 1990s.

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. But, someone said that a 128 or 128D 
keyboard featured a low-resistance left shift key.


       Message was sent through the cbm-hackers mailing list
Received on 2011-12-09 10:00:04

Archive generated by hypermail 2.2.0.