[sdiy] Another SID-related question

[Gordonjcp]

On Tue, Jul 29, 2025 at 02:40:22PM +0300, Antti Pitkämäki via Synth-diy wrote:
> 
> The basic idea for the mod is to connect an extra circuit board to the
> original SID chip socket, which provides most of the required connections.
> The SID only "listens" to the five least significant address lines. Hence,
> in a stock C64 separate glue logic is utilized to provide the chip select
> signal for the SID when memory locations allocated to it are accessed. In
> my mod I'll use a 74LS138 decoder, enabled by the original chip select
> signal. Two additional address lines will be connected to its inputs and
> its outputs will be connected to the SIDs' chip selects, placing each SID
> in its own dedicated memory space. With this system it would be very easy
> to add up to 8 SIDs if I wanted to go totally crazy. But four SIDs for now
> :)

In the olden days we sometimes expanded memory by stacking RAM chips on top of the one already on the PCB, and bringing the /CS lines out to another address decoder.

-- 
Gordonjcp