Panasoft SW-M004
This page was last modified 19:40, 26 May 2023 by Mars2000you. Based on work by FiXato and Gdx and others.




The SW-M004 is a cartridge called FM-PAC (FM Pana Amusement Cartridge) which was introduced by Panasonic in 1988. 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 Yamaha YM2413 sound chip with its specific BIOS (MSX-MUSIC BASIC), and an 8kB SRAM chip for saving game data (fully compatible with the PAC cartridge).

The 8kB is arbitrarily divided into 8 pages of 1024 Bytes each. A game may use one or more pages to save its data.

Some games allow you to select which pages to use, others are hardcoded to use specific pages. It is up to the user to ensure he does not overwrite old save states from the game, or save states of other games. Method access to SRAM is described here.

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.

You can also use folling software that is a alternate tool to backup and restore the SRAM content:

This firmware is in Japanese but you can translate it by changing the Rom. The patch can be downloaded from downloads here.



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
  • 8kB SRAM (just like the Panasoft 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 non-rechargeable 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 by soldering a new one (type: CR2025 or BR2025 Lithium 3V). Confirmation is needed about battery pins type. Be careful not to overheat the battery when soldering it, and put on safety glasses because of the risk of explosion with heat.

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

PAC Logo
PAC Logo translated
PAC Logo
PAC Logo translated
Additional PAC Logo to indicate the game needs block 8 only
Additional PAC Logo to indicate the game needs block 1-4 only

Software using the PAC to save data

See the list here.

External links