[sdiy] Another SID-related question

[Antti Pitkämäki]

"Piggybacking" is one way to approach this mod - in fact, Hermit, the
author of the native C64 music tracker for 4 SIDs, modded a C64 for 3 SIDs
with the piggybacking approach. I'll use stripboard :)

Antti

On Tue, Jul 29, 2025 at 10:05 PM Gordonjcp <gordonjcp at gjcp.net> wrote:

> 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
>
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