CONFIG tool for SIDFX

Last updated: 2016-10-08 (version 4)

SIDFX has the following operating modes:

Mono: Auto

This is the factory default.

When two SIDs are installed it operates in "Mono: SID1+SID2" mode, otherwise in "Mono: SID1 only" mode.

Mono: SID1 only

SID1 and SID2 are both located at $D400. SID register writes go to both SIDs, and SID register reads come from SID1.

Both audio channels come from SID1, provided that switch #1 is in the CENTER position (see switch #1 control for more details).

Because both SIDs receive the same writes they are both playing.

Switch #1 can be used to force the audio output to come from SID1 (LEFT position) or SID2 (RIGHT position).

Mono: SID2 only

SID1 and SID2 are both located at $D400. SID register writes go to both SIDs, and SID register reads come from SID2.

Both audio channels come from SID2, provided that switch #1 is in the CENTER position (see switch #1 control for more details).

Because both SIDs receive the same writes they are both playing.

Switch #1 can be used to force the audio output to come from SID1 (LEFT position) or SID2 (RIGHT position).

Note: POTX/POTY register reads always come from SID1 (where those hardware signals are connected) in order to not disturb paddle operations.

Mono: SID1+SID2

SID1 and SID2 are both located at $D400. SID register writes go to both SIDs, and SID register reads come from SID1.

The left audio channel comes from SID1 and the right audio channel comes from SID2, provided that switch #1 is in the CENTER position (see switch #1 control for more details).

Because both SIDs receive the same writes they are both playing.

Switch #1 can be used to force the audio output to come from SID1 (LEFT position) or SID2 (RIGHT position).


Stereo: SID2 at $D420

SID1 is located at $D400 and SID2 at $D420. SID register writes go to the individual SID being addressed, and SID register reads come from the individual SID being addressed.

The left audio channel comes from SID1 and the right audio channel comes from SID2, provided that switch #1 is in the CENTER position.

Switch #1 can be used to force the audio output to come from SID1 (LEFT position) or SID2 (RIGHT position).

Note: POTX/POTY register reads come from the individual SID being addressed. The POTX/POTY pins of SID2 are not connected and will as a result return 0x00.

Stereo: SID2 at $D500

SID1 is located at $D400 and SID2 at $D500. SID register writes go to the individual SID being addressed, and SID register reads come from the individual SID being addressed.

The left audio channel comes from SID1 and the right audio channel comes from SID2, provided that switch #1 is in the CENTER position.

Switch #1 can be used to force the audio output to come from SID1 (LEFT position) or SID2 (RIGHT position).

Note: POTX/POTY register reads come from the individual SID being addressed. The POTX/POTY pins of SID2 are not connected and will as a result return 0x00.

Stereo: SID2 at $DE00

SID1 is located at $D400 and SID2 at $DE00. SID register writes go to the individual SID being addressed, and SID register reads are ignored.

The left audio channel comes from SID1 and the right audio channel comes from SID2, provided that switch #1 is in the CENTER position.

Switch #1 can be used to force the audio output to come from SID1 (LEFT position) or SID2 (RIGHT position).

Note: POTX/POTY register reads come from the individual SID being addressed. POTX/POTY register reads from SID2 are currently being ignored by SIDFX (see below).

Note: To ensure compatibility with cartridge expansions all register reads from the $DE00 memory space are currently being ignored by SIDFX.

If a cartridge is installed the cartridge may respond with data, otherwise random bus data are returned. This behavior ensures that bus conflicts do not occur, which would otherwise lead to unstable operation or potentially cause damage to SIDFX and/or the expansion cartridge.

Note: $DE00 is the address mapping that MSSIAH requires to work.


External Input (Mute/Enable)

The EXTIN audio input signal from the C64 A/V connector which is normally connected to the SID may be disconnected (muted) in order to reduce noise.

The factory default setting is muted

For the best results we recommend only enabling External Input in case you are actively using it.

SID Type (Auto/6581/8680/None)

The SID type can be configured automatically or manually.

The factory default setting is automatic.

In automatic mode SIDFX will auto-detect the SID types at power-on and set the operating voltages, filter capacitor values etc. accordingly.

In manual mode the user may set the SID type to 6581, 8580 or NONE, forcing SIDFX to detect and report a different type. This is only recommended for expert users, because an incorrect setting may cause damage to you SID chip.

Note: Manual SID Type configuration is currently disabled.

Digi-boost Mode (Auto/Permanent) and Digi-boost Loudness (+0dB to +21dB)

These features control if/how/how much the 8580 output level is increased during playback of samples generated using the SID volume register.

3 scenarios are possible:

  • Permanently off (Mode=Permanent and Loudness=+0dB): This setting operates like a factory 8580.
  • Permanently on (Mode=Permanent and Loudness=xxdB): This setting operates like a factory 8580 patched with an external resistor from the EXTIN pin to GND. Depending on the loudness setting (or resistor value) this may alter how regular SID music sounds, so this setting is not recommended for normal use.
  • Smart enable (Mode=Automatic and Loudness=xxdB): This setting automatically enables digi-boost during sample playback (SID volume register written more than around 800 times per second), and thus won’t alter how regular SID music sounds. This is the recommended setting.

The Loudness setting (Loudness=xxdB) is used to specify how much the samples should be boosted. Some 8580 play samples well without boosting while others are heavily attenuated. For reasons explained above you should not excessively boost the samples, as it may alter how the 3 regular SID channels sound (in case of 4 channel music).