Re: Additional SIDs

From: Gerrit Heitsch <>
Date: Thu, 01 Dec 2011 18:58:43 +0100
Message-ID: <>
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.


       Message was sent through the cbm-hackers mailing list
Received on 2011-12-01 18:00:31

Archive generated by hypermail 2.2.0.