YM2612 Basics

This page is a browser-readable version of the early YM2612 notes in this repository. The focus is the minimum path from chip pins to a simple beep.

Pin Layout

    +--()--+
GND | 1  24| 0M(CLK)
 D0 | 2  23| Vcc
 D1 | 3  22| A.Vcc
 D2 | 4  21| MOL
 D3 | 5  20| MOR
 D4 | 6  19| A.GND
 D5 | 7  18| A1
 D6 | 8  17| A0
 D7 | 9  16| /RD
  ? |10  15| /WR
/IC |11  14| /CS
GND |12  13| /IRQ
    +------+

Pin Summary

GND: digital ground
A.GND: analog ground for audio output
Vcc: digital power supply
A.Vcc: analog power supply for audio output
MOL / MOR: left / right audio outputs
D0-D7: 8-bit bidirectional data bus
A0 / A1: port select pins
/RD, /WR, /CS, /IRQ, /IC: control signals

A0 and A1

A0 and A1 select address/data access and port 0 / port 1.

A1=0, A0=0: address port 0
A1=0, A0=1: data port 0
A1=1, A0=0: address port 1
A1=1, A0=1: data port 1

How `chip.write()` Maps to Pins

void ym2612::write(uint32_t offset, uint8_t data) is a simplified software interface.

offset = 0: address port 0
offset = 1: data port 0
offset = 2: address port 1
offset = 3: data port 1

chip.write(0, 0x30);
chip.write(1, 0x01);

This means: select register 0x30, then write 0x01 into it.

What We Do to Make a Beep

Create a ym2612 object.
Reset the chip.
Set operator parameters for channel 1.
Set algorithm and stereo output.
Set frequency.
Send key on.
Generate samples.

Key Register Groups

0x30-0x3c: detune and multiple
0x40-0x4c: total level
0x50-0x5c: attack rate
0x80-0x8c: sustain level and release rate
0xb0: algorithm and feedback
0xb4: left/right output enable
0xa4 and 0xa0: frequency
0x28: key on / key off

Why Algorithm 7?

Algorithm 7 is a simple starting point because all 4 operators act as carriers. Every operator directly contributes to the output.

Good Next Reads

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