Re: Blurry picture

From: Segher Boessenkool <>
Date: Sat, 19 Nov 2011 18:16:28 +0100
Message-Id: <>
>> and they use
>> a very different PLA (or custom chip actually, for the C64C).  The  
>> 82S100
>> PLA used in the C64 has a propagation delay of typical 40ns, max.  
>> 80ns.
> The C64C uses a LH5062 Sharp CMOS part.  It might well be faster, but
> who knows.
> My current theory is all the components are just a little different,
> and it all conspires to make R/#W or #CS too early :-)

The 82S100 PLA contains an interesting unused minterm:

#CAS=1, A15..A12=1101, #AEC=0, R/#W=0

i.e. the first half of a write cycle from the CPU to I/O space.  That
is exactly when it is not okay to write to the VIC, since that exposes
its registers to its precharged bus.  Interesting :-)


       Message was sent through the cbm-hackers mailing list
Received on 2011-11-19 18:00:08

Archive generated by hypermail 2.2.0.