Skip to content

SFX

Jump to bottom
LGB Z edited this page Mar 18, 2015 · 3 revisions

The SFX Sound Expander cartridge for C64

This cartridge allowed for C64 to have even more music capabilities than using its SID chip. Please read this wiki entry as well.

However we need YM3812 chip as it's described here.

Additional information on this hardware: http://www.floodgap.com/retrobits/ckb/secret/sfx.html

More hardware related information (including the possibility to build an SFX Cartridge compatible stuff using a spare AdLib ISA card for PC): hardware.

Details

Anyway in nutshell: it seems, using the cartridge for playback is really simple. Like with AdLib, where you have I/O ports 388h and 389h, but you must use the following memory addresses instead:

  • $DF40: selects the register
  • $DF50: write (or read?) the selected register

If you have YM3812 chip installed on your cartridge, this basically means that you have an "AdLib" card, just you have to use the mentioned memory locations instad of the I/O ports would be used on a PC with an AdLib cart. Also, the timing is similar: you have to wait some time between register accesses. From the mentioned resource, the following method is suggested:

; load x with register, a with data for that register
  stx $df40               ; select ym3526 register
  nop
  nop
  nop
  nop                     ; wait 12 cycles for register select
  sta $df50               ; write to it
  ldx #4
lup: 
  dex
  nop
  bne lup                 ; wait 36 cycles to do the next write

Of course, if you have enough code between the accesses anyway, you don't need the dedicated wait.

Currently I am not interesed in other nice features of the cartridge, like the piano-keyboard which can be also queried from your program.

About the meaning of the registers you can select then read/write: it's really same as with AdLib, so any AdLib documentation can tell that (again: it's true if you have YM3812 chip installed. If not, some features will be missed, no OPL2, also the AdLib's detection method described by some resources won't work with the C64 then!). For more information, visit the link can be found on this page.

Clone this wiki locally