MOS 6502 6522 6560 ICs in a VIC-20

Context: Besides a custom kernel initially written for the Commodore PET by John Feagans and further developed by Robert Russell, plus a $10,000 version of Micro-Soft "BASIC V2" (that Commodore shamelessly used in about 20 Million computers), and an extended ASCII character set (PETSCII), the VIC-20's hardware foundation is built upon 4 x 40-pin custom integrated circuits made by MOS Technology. Commodore purchased the company in 1976, and these critical chips are discussed below. The VIC-20 had a four year product life-span from January 1981 to January 1985, and Bill Seiler was the top notch hardware guy who really made all of the original hardware stick together.

The 6502 (locate blue dot in schematic above) is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. Unit cost was targeted to be $25, so it was the least expensive full-featured microprocessor on the market. It sparked a series of computer projects that would eventually result in the home computer revolution of the 1980s, though its design was never originally intended to be used in a personal computer. The chip featured some industry firsts: N-channel design and layout (with zero errors); pipelining; and non-contact mask liners in fabrication. The 6502 design, with about 4,000 transistors, was second-sourced by Rockwell and Synertek, and the 6500 family ended up being used in products from Apple, Atari, Nintendo, BBC Micro and numerous others. It is one of those rare products that fundamentally changed the world. Mr. Mensch and the legendary 6500 family are still going strong over at the Western Design Center.	Datasheet 6502/10 Information 65xx Series Information Kernel Differences

The 6522 Versatile Interface Adapter (locate green dots in schematic above) was an integrated circuit made by MOS Technology, as well as second sourced by Rockwell and Synertek. The VIA was first conceived by Chuck Peddle in 1974. It served as an I/O port controller for the 6500 family of microprocessors, providing parallel I/O capabilities as well as timers and a shift register for serial communications. (Combine a 6522 with a 6502 and you have the basis of a functional computer.) The 6522 was very popular in computers of the 1980s including the Apple Macintosh. In the VIC 20 the VIA provided for some innovative features like the User Port and a low-cost Serial Bus for disk drives and printers. These days the 6522 VIA supports an ethernet adapter on my VIC's user port; a CD player attached to the cassette port and and SD card slot attached to the serial port. Truly extensible architecture!	Datasheet VIC-20 Specific VIA Information VIC-20 Specific VIA Register Usage 6522 VIA "bug" (see: CB2 sound) The Serial Bus

The Video Interface Chip (locate red dot in schematic above), specifically known as the MOS Technology 6560 (NTSC version) / 6561 (PAL version), is the integrated circuit chip responsible for generating video graphics and sound. It was originally intended for applications such as low cost CRT terminals, biomedical monitors, control system displays and arcade or home video game consoles. The chip was designed by Al Charpentier in 1977 and refreshed by Bob Yannes before being mass produced in the Commodore VIC-20. (2.5 Million units by the end of production.) In the VIC-20 the GPU was the "master" and the CPU was the "slave" accessing memory during alternate phases, so both chips could run at full speed with exclusive access to memory. Besides this technological brilliance, the VIC also allowed for custom character sets that could be modified by end users -- another industry first. Today people are still pushing this little chip to do things never imagined back in the 1980s, including a mouse-driven GUI and 208x256x16 color graphics. This demo even won 1st place at the alternative demo compo at The Alternative Party in 2010.	Datasheet "VIC" Chip Information Additional "VIC" Chip Information "VIC" Chip Register Usage "VIC" Chip Tables

Circuit Board Photos by Jeff Salzman