|Video Interface Chip|
1.) Square Wave
The Video Interface Chip (VIC) is the defining chip of the Commodore VIC 20 series of 8-bit home computers. It handles graphics, movements of a plugged-in mouse, paddle or light gun, and audio.
On each of four channels, you can choose a pitch in 128 steps, down to roughly C♯1. Every channel is one octave higher than the other. The fourth channel is supposed to be noise, although it still sounds a bit melodic.
For all four channels together, you can only choose one volume, from 0 to 15. Changing the volume produces a click; the greater the change, the louder. This allows to play unsigned 4-bit PCM samples on a fifth channel. The VGMPF currently does not know if any game does that.
Commodore's datasheet specifies to clock the 6560 at 14.31818 MHz for NTSC standard.
The 6560 divides its clock by 14 to determine the CPU clock, and further by 65×261 to determine the screen refresh rate.
Commodore's datasheet specifies to clock the 6561 at 4.436187 MHz (obviously a typo, where a 3 was omitted) for PAL standard.
The 6561 divides its clock by 4 to determine the CPU clock, and further by 71×312 to determine the screen refresh rate.
|1981-??-??||VIC 20 (NTSC)||6560|
|1981-??-??||VIC 20 (PAL)||6561|
Several VIC 20 games play music and sound effects on the VIC.
VICE 3.2 accurately emulates the VIC 20 (NTSC and PAL).