Yamaha S1985
This page was last modified 13:59, 14 April 2023 by Mars2000you. Based on work by Gdx and Grauw and others.


Yamaha S1985

The S1985 is a chipset called MSX-SYSTEMII made by Yamaha for ASCII. It is similar to the S3527 with some optional features in extra.

The features are:

  • a Yamaha YM2149 PSG-sound chip, compatible with a General Instrument AY-3-8910 (for sound, joystick ports, etc) with stereo output (A: Center, B: Left, C: Right).
  • PPI: backward compatible with the Intel i8255 (for primary/secondary slot selection, keyboard (keypad included), cassette interface, etc)
  • other MSX functions: DRAM/ROM control, printer interface, etc.
  • Memory Mapper (up to 512kB )
  • Real Time Clock (Ricoh RP5C01A compatible) including 26 x 4 bits RAM, backed up by (separate) battery
  • Backup RAM (8 bit x 16)
  • 100 pin flat plastic package


  • The S1985 makes a mirror of VDP ports 98h-9Bh to 9Ch-9Fh.
  • All 3 PPI ports (0a8-aah) and control port (0abh) are mirrored to I/O ports 0ac-0afh. This can be used to determine if a machine has an MSX-ENGINE.

Computers with the S1985