FPGASID in SammichSID?

dualmono · May 14, 2020, 12:16pm

Did anyone install FPGASIDs in their sammichSID?
I’m looking for replacements for my 8580s and was wondering if sammichSID would be compatible to FPGASID and if it would be possible to use one FPGASID to replace both sammichSID ICs?
And if it is possible, how to do it.

Thanks!

Fab · June 3, 2020, 9:41pm

I’ve not done this, but I did ask Andi of the FPGASID project the same question and he sent this reply:

“Yes, I think this should be possible. FPGASID can be configured in a way
that it listens to two separate chip select lines that are used to
select one or the other internal SID. As far as I have seen in MidiBox
schematics so far, the two SID sockets are conntected to a single data
and address bus and only the chip select lines are separated for the two
SIDs. Such a scenario can be supported by FPGASID. Many people do the
same thing on the Ultimate64 which is a FPGA-based C64 but with two SID
sockets.

These steps would have to be done:

Use a C64 to configure the FPGASID to stereo mode with the Address
DE00 enabled and all other adresses disabled. Then save the
configuration to flash mem A (power up default)
Plug the FPGASID into one of the sockets
Connect the chip select signal of the second socket to the red wire
of the 3-wire-cable of the FPGASID (DE00 chip select signal)
Connect the raw-audio signal of the FPGASID (solder eye on the
FPGASID PCB) to the AUDIO signal of the second SID socket.
That should do it.

There are some constraints to consider:
* The FPGASID has only one single external audio input and ony pair of
paddles that are shared between both SIDs inside FPGASID.
* You will need some control software as part of the MidiBox software to
change the FPGASID settings (switching between 8580 and 6581 mode etc)
in case you whish to do so.
* You will need a C64 for step 1 OR, in case you do not have one, you
will need special setup function in the Midibox software to enable
stereo mode each time it powers up.”

This is beyond my abilities though (there’s a reason I went for the sammichSID over a ground up midi box), so I was coming here to see if anyone had any ideas on how to implement this.

Noise-Generator · June 4, 2020, 10:46am

12 hours ago, Fab said:

This is beyond my abilities though (there’s a reason I went for the sammichSID over a ground up midi box), so I was coming here to see if anyone had any ideas on how to implement this.

You mean implementing the software?

* You will need some control software as part of the MidiBox software to
change the FPGASID settings (switching between 8580 and 6581 mode etc)
in case you whish to do so.

—

I think it’s possible that somebody could implement some code to switch the fpgasid from 8580 to 6581 with the Midibox

BUT

Each SID Version needs different Filter Caps and a different Filter table provided by the firmware. Building a code which would change the Filter table, maybe possible (if there is space left in the PIC), but you also must change the Filter Caps by opening the box or maybe build an extra analog circuit for the Caps which than need a switch.

You also need to know, the sammich is a stereo SID solution, both SIDs are handled like the same (2x8580 or 2x6581)

It´ s more complicated than it seems, unfortunately.

Pedech · July 14, 2021, 12:42am

On 5/14/2020 at 9:16 AM, dualmono said:

Did anyone install FPGASIDs in their sammichSID?
I’m looking for replacements for my 8580s and was wondering if sammichSID would be compatible to FPGASID and if it would be possible to use one FPGASID to replace both sammichSID ICs?
And if it is possible, how to do it.

Thanks!

Just did it. One FPGASID replacing both ICs. You can define using a C64 what mix of SIDs you want the Fpgasid to emulate.

I just followed the steps posted by , ignoring the mentioned control software step.