On 12/01/2011 06:24 PM, Richard Atkinson wrote: > Strikes me $D7xx is the best place for an internal SID modification, > being as that is spare in the C128 and actually decoded. No idea who > decided $D420 was a good idea, that takes way more in the way of address > decoding. Obviously easier in this day of programmable logic devices, > but what about a good old 74LS139 for decoding $D400 further? Should be simple... You connect _E of the 74LS139 to the original SID _CS, hardwire input 1 of the decoder to GND and connect the input 0 to A5. That should give you 2 chip selects for 2 SIDs, one for $D400 and one for $D420 (plus some mirror images of them until $D7FF). That way the 2 SIDs appear directly after each other in the address space. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2011-12-01 18:00:31
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