Yamaha YIS-503IIR
This page was last modified 16:29, 2 January 2018 by Mars2000you. Based on work by Rderooy and Msxholder and others.



The Yamaha YIS-503IIR is the adaptation of the YIS-503II or the CX11 computer for Soviet Union. It was not sold in shops and could only be used in schools. The "КУВТ" logo is the abbreviation of "Комплект учебной вычислительной техники" and means "Class of Teaching Computing Equipment".

This computer has a Russian keyboard and the specific music connectors have been replaced by 2 serial port connectors and a switch allowing the machine to work in teacher mode or in student mode. The communication between MSX computers is actually controlled by a RS-232C interface.

By default, the network firmware is enabled and the content of the function keys is modified for F1 and F6 to F10:

Key Display Command Key Display Command
F1 color COLOR F6 run"COM:" RUN"COM:"
F2 auto AUTO F7 save"COM:" SAVE"COM:"
F3 goto GOTO F8 load"COM:" LOAD"COM:"
F4 list LIST F9 merge"COM:" MERGE"COM:"

In this system, several student machines are connected to a teacher machine with an external floppy disk drive for centralised file storage. Note that the corresponding machine for the teacher in the blueMSX emulator includes an internal floppy drive.

The network firmware can be disabled by pressing DEL key while booting. It is recommended to disable it for playing games, this to avoid eventual incompatibility, or for using the machine as a standard MSX with the 'normal' content of the function keys.

Brand Yamaha
Type YIS-503IIR
Year 1985
RAM 64kB in slot 3-2
Media MSX cartridges, (only teacher machine) DD floppy disks
Video Yamaha V9938 (MSX2 VDP!)
Audio PSG (YM2149 integrated in MSX-Engine S3527)
Chipset Yamaha S3527
Extras Internal RAM / VRAM expandable, RS-232C interface + switch + RS-232C BASIC, (only teacher machine) 1 external 720kB 3,5" floppy disk drive


Yamaha YIS-503IIR
Yamaha YIS-503IIR back
Yamaha YIS-503IIR Main PCB
Yamaha YIS-503IIR left side
Yamaha YIS-503IIR RAM board
Yamaha YIS-503IIR VRAM board


The YIS-503IIR is a MSX1 with a Z80A from Sharp (LH0080A), a V9938 and an MSX-Engine S3527 from Yamaha.

This computer can be easily upgraded internally because RAM and VRAM are each on an daughterboard. Simply just to change the corresponding board.


  • RGB output
  • Analog sound & Composite video (color NTSC)
  • Tape recorder connector
  • Centronics compatible Parallel port for a printer
  • 2 general connectors (joysticks, mouse, paddle controllers, ...)
  • 2 cartridge slots
  • 2 serial port connectors