>> 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 :-) Segher Message was sent through the cbm-hackers mailing listReceived on 2011-11-19 18:00:08
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