NerdyPOKEY

Hello! This application provides a built-in 6502 assembler and POKEY emulator for runnable examples. The SAP file is dynamically built from the editor contents, so you can change things and hear the result. We will build a simple sound engine in incremental steps.

1 - Playing a square wave

AUDCTL (Audio Control byte) - $D208

This byte sets the global configuration.

76543210
||||||||
|||||||+- Clock base (0: 64KHz, 1: 15KHz)
||||||+-- Filter channel 2 (clocked by channel 4)
|||||+--- Filter channel 1 (clocked by channel 3)
||||+---- Link channels 3 and 4
|||+----- Link channels 1 and 2
||+------ Clock channel 3 at 1.79MHz
|+------- Clock channel 1 at 1.79MHz
+-------- Poly counter (0: 17 bit, 1: 9 bit)

AUDC (Control registers) - $D201, 3, 5, 7

These registers control each channel's volume and distortion waveform.

76543210
||||||||
||||++++- Volume
|||+----- Volume-only mode
||+------ 0: noise, 1: square wave
|+------- 0: 9/17 bit poly, 1: 4-bit poly
+-------- Sampling mode (0: 5-bit poly, 1: 4/9/17-bit poly)

AUDF (Frequency registers) - $D200, 2, 4, 6

The clock rate is divided by this value to determine the channel's pitch.