The YM2203, a.k.a. OPN (FM Operator Type-N), is a three-channel sound chip developed by Yamaha. It was the progenitor of Yamaha's OPN family of FM synthesis chips used in many videogame and computer systems throughout the 1980s and early 1990s. The YM2203 itself was used in a variety of NEC computers, along with various arcade game machines.
The YM2203 and the rest of the OPN synthesizer family generate sound via frequency-modulated digital sine waves. It included 12 operator "cells", each generating a 13-bit sine wave at a programmable frequency, the volume of which is controlled by a programmable ADSR envelope generator. The output of these cells could be either summed together by the mixer, or fed into the input of another cell, in 4-cell batches creating the final sound values or "channels". 4 operator cells per channel allowed a total of 8 different permutations of cell connections, known as "algorithms" or instrument patches.
The YM2203 has the following features:
- Three concurrent FM channels (voices)
- Four operators per channel
- Two interval timers
- Mono sound internal implementation of Yamaha's YM2149F SSG chip
The SSG module implemented the YM2149F's three SSG channels and dual GPIO ports
The YM2203 is used with a YM3014 external DAC companion chip.