Panasoft FM-PAC
This page was last modified 16:20, 29 June 2021 by Mars2000you. Based on work by Gdx and SPMNT and others.




The FM-PAC (FM Pana Amusement Cartridge) is an FM sound synthesizer cartridge which was introduced by Panasonic in 1988 (part number SW-M004). It is the only official MSX-MUSIC cartridge expansion and was released under the Panasoft brand, used by Panasonic for some software.

The cartridge contains the MSX-MUSIC chip with its specific BIOS (MSX-MUSIC BASIC), and an SRAM chip for saving game states (compatible with the PAC cartridge). A hardware switch allows the user to choose between three possible output volumes for the MSX-MUSIC sound, which is mono.

Release price: ¥7.800


The cartridge also has built-in software, which can be started by running CALL FMPAC or _FMPAC from BASIC. Here the user can listen to various demo sounds, and backup and restore the SRAM content. In the BGM (Back Ground Music) menu option, one can press TAB to get a virtual music keyboard and play the FM-PAC as a musical instrument.



Panasoft FM-PAC Cartridge scan
Panasonic FM-PAC full package
Panasonic FM-PAC cartridge
SW-M004 PCB front with removed button cell
SW-M004 PCB front
SW-M004 PCB back


Main Menu
Option 1: Clear
Option 2: Copy
Option 3: Change
Option 4: Delete file
Option 5: Slot
Option 6: BGM
Music keyboard


  • YM2413 FM chip
  • 16kB MSX-MUSIC Basic
  • 4kB SRAM (just like the Panasonic SW-M001 PAC)
  • Volume adjuster
  • Mono sound output
  • Built-in firmware

See MSX-MUSIC page for more specifications.


The FM-PAC (and likewise the Panasoft PAC) has a battery, without it the SRAM will not keep the contents when the system is switched off. This coin cell battery can be replaced, you need to open the cartridge and replace the battery with a new one (type: Panasonic BR2325 Lithium 3V). See this thread for details.

Typically a PAC compatible game will have one of these logo's on the box. They may also indicate which save slots they need.

PAC Logo
PAC Logo
PAC Logo, indicating the game needs slot 8
PAC Logo, indicating the game needs slot 1-4

External links