Re: 6567 revisions (was Re: 264/TED/Plus4 Story)

From: Segher Boessenkool <>
Date: Thu, 25 Aug 2011 21:32:50 +0200
Message-Id: <>
> Hmm, now I got another question: What was the mysterious "always  
> set this bit to 0" in the VIC-II? Was it used in some early 6567  
> revision? I do not remember any effect when I set it on any of the  
> 6567 or 6569 that I had.
>   D016       53270                 VIC Control Register
> 			    7-6    Unused
> 			    5      ALWAYS SET THIS BIT TO 0 !
> 			    4      Multi-Color Mode: 1 = Enable (Text or
> 				     Bit-Map)
> 			    3      Select 38/40 Column Text Display:
> 				     1 = 40 Cols
> 			    2-0    Smooth Scroll to X Pos

That's the RESET bit.  On the 8565R2, it's a register bit but not  
to anything; on the 6569R1, it's a register bit that connects to a  
end of metal and poly, well with a cut actually, and then ends  
nowhere, not
clear where it would go.

Supposedly this bit had a function on the predecessor to the VIC-II, the
6566(?), which was SRAM instead of DRAM.  It's quite clear on the  
6569 that
the DRAM stuff (address muxes, RAS/CAS, etc.) was tucked on; on the 8565
it's cleaned up a bit (it has a different pad ring).

Perhaps RESET stopped all memory accesses, and/or forced the X and/or Y
counters to 0.  If anyone has such a chip, feel free to send it to
visual6502 for picturing and analysis :-)

> This is not to be confused with the C128 VIC-IIe test mode bit in  
> $d02f or $d030 that really does something. This would not be the  
> first bit that has been disabled in a Commodore video chip. In the  
> NTSC VIC-I, there is a bit for enabling interlace mode. It does not  
> work in the PAL VIC-I.  I wrote a test program for it: look for  
> interlace.prg and interlace.tar.gz at 
> pub/cbm/vic20/programming/.

We have a 6561 as well...  Let's see, reg 00 bit 7...  It's wired up,  
to the Y decoder, and the one output from there is wired up as well.   
I don't
have further details, I haven't fully reversed this chip (yet).  I  
guess the
interlace doesn't work as intended, but it's still there?


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Received on 2011-08-25 20:00:29

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