Merge pull request #313 from nicco1690/patch-3

Create VIC-20 documentation

papers/doc/7-systems/README.md

@@ -27,5 +27,6 @@ this is a list of systems that Furnace supports, including each system's effects
 - [Yamaha OPL](opl.md)
 - [PC Speaker](pcspkr.md)
 - [Commodore PET](pet.md)
+- [Commodore VIC-20](vic20.md)
 
 Furnace also reads .dmf files with the [Yamaha YMU759](ymu759.md) system, but...

papers/doc/7-systems/vic20.md

@@ -0,0 +1,11 @@
+# Commodore VIC-20
+
+The Commodore VIC-20 was Commodore's major attempt at making a personal home computer, and is the percursor to the Commodore 64. The VIC-20 was also known as the VC-20 in Germany, and the VIC-1001 in Japan.
+
+It has 4 PSG voices that has a limited but wide tuning range, and like the SN76489, the last voice is dedicated to playing pseudo-white noise. Every voice on the VIC-20 has a high-pass and low-pass filter applied to it, which is likely how Rob Yannes got the inspiration to put custom filter modes on the C64's SID.
+
+The 3 pulse wave channels also have different octaves that they can play notes on (not currently emulated in Furnace version dev71). The first channel is the bass channel, and it can play notes from octaves 2 to octaves 4. The next is the 'mid/chord' channel, and it plays notes from octaves 3 to 5. And rather obviously, the 3rd pulse channel is typically the lead channel, can play notes from octaves 4 to 6.
+
+## effect commands
+
+ - `10xx` Switch waveform (Only the values 00 though 0F are unique. Everything else is a copy. For example, `1006` is the same as `10f6`.)