This page was last modified 14:27, 10 October 2021 by Mars2000you.


JJFS BASIC is an extension that comes with the JJFS.ROM included in the JJFS zip file created by the Japanese fan Tiny Yarou.

It can be used on any MSX with at least 64kB RAM (If you burn it to ROM, it will work on any MSX with at least 8kB RAM). You can download it here.

Links :

JJFS means Joy Joy File System, it allows to communicate between

  • two MSX computers by connecting their joystick ports 2
  • MSX and PC (Windows) computers by connecting the joystick port 2 of the MSX and the RS-232C port of the PC

A specific cable is required. This system was inspired by the Joy232 project of the Brasilian fan Danjovic. It allows data communication at 38400 bps.


  • Make first the above mentioned connection between MSX and PC (Windows)
  • On PC: run JoyJoyFileServer.exe, then click on Connect
  • On MSX: execute JJFS.BAS (note: WAV versions are also provided)
  • ON PC: click on Install


This extension adds 17 new instructions.

Note: CALL can be replaced by the character underscore (_). A space is not required after this character. See CALL for more info.

Instruction Generation Type
CALL JJBLOAD MSX1 PC → MSX transfer instructions
CALL JJBSAVE MSX1 MSX → PC transfer instructions
CALL JJCHGCPU Turbo R General instructions
CALL JJDLOAD MSX1 Floppy disk instructions
CALL JJDSAVE MSX1 Floppy disk instructions
CALL JJDUMP MSX1 Debug instruction
CALL JJFILESIZE MSX1 General instructions
CALL JJINPUT MSX1 Synchronization instruction
CALL JJLOAD MSX1 PC → MSX transfer instructions
CALL JJRECV MSX1 General instructions
CALL JJRECVBYTE MSX1 General instructions
CALL JJRECVMSG MSX1 General instructions
CALL JJSAVE MSX1 MSX → PC transfer instructions
CALL JJSEND MSX1 General instructions
CALL JJSENDBYTE MSX1 General instructions
CALL JJSENDMSG MSX1 General instructions
CALL JJVRAMPAGE MSX2 VRAM control instruction