Commodore VIC-20

Commodore VIC-20
	Commodore VIC-20 – The Friendly Computer
Specifications
Manufacturer	Commodore Business Machines
Type	Home Computer
Released	1980 (Japan), 1981 (Worldwide)
Discontinued	January 1985
Intro price	US$299.95 (1981)
CPU	MOS Technology 6502 @ 1.1 MHz (PAL) / 1.02 MHz (NTSC)
Memory	5 KB RAM (3.5 KB usable), expandable up to 32 KB
Storage	External cassette tape (Datasette), optional 5.25" floppy disk drive
Display	176×184 pixels, 22×23 text characters, 16 colors
Sound	3 square wave generators + 1 noise channel (mono)
Dimensions	40.3 cm × 20.4 cm × 7.2 cm
Weight	1.8 kg
OS / Firmware	Commodore BASIC 2.0 (in ROM)
Predecessor	Commodore PET 4000 Series
Successor	Commodore 64
Codename	VIC-20, VC-20 (Germany), VIC-1001 (Japan)
Model no.	VIC-1001, VIC-20, VC-20

The Commodore VIC-20 was a groundbreaking home computer introduced by Commodore Business Machines in 1980. Known as the VIC-1001 in Japan and the VC-20 in Germany, it was the first computer to sell over one million units, making computing accessible to the masses.

Architecture and Processor

At its core, the VIC-20 utilized the MOS Technology 6502 8-bit microprocessor, operating at 1.1 MHz for PAL systems and 1.02 MHz for NTSC systems. This CPU was also employed in other notable systems like the Apple II and Commodore 64.

Memory and Storage

The VIC-20 came with 5 KB of RAM, with approximately 3.5 KB available for user programs. Memory could be expanded up to 32 KB via external cartridges.

For storage, the VIC-20 relied on external devices:

Datasette – a cassette tape drive for loading and saving programs.
VIC-1540/VIC-1541 – optional 5.25" floppy disk drives connected via the serial port.

Display and Graphics

The VIC-20 featured a 176×184 pixel resolution with a text display of 22 columns by 23 rows. It supported a palette of 16 colors. Graphics were character-based, and while it lacked a bitmap mode, users could define custom characters for simple graphics and animations.

Sound Capabilities

Sound was generated through the MOS Technology VIC chip, offering:

Three square wave generators.
One white noise generator.
Overall volume control.

These features allowed for basic music and sound effects in games and applications.

Input/Output and Expansion

The VIC-20 was equipped with several I/O ports:

Cartridge Port – for software and memory expansion cartridges.
User Port – for modems and user-designed peripherals.
Serial Port – for printers and disk drives.
Joystick Port – compatible with Atari-style joysticks.
Cassette Port – for the Datasette.
RF and Composite Video Outputs – for connection to TVs and monitors.

General Maintenance

Over time, VIC-20 computers may experience issues common to vintage electronics, such as:

Aging capacitors leading to power supply instability or failure.
Keyboard contact wear causing unresponsive or erratic key behavior.
Overheating of the linear voltage regulator (LM323K), potentially leading to case deformation or component damage.
Degradation of the RF modulator affecting video output quality.

Regular maintenance, including capacitor replacement, keyboard cleaning, and ensuring proper heat dissipation, can help preserve the functionality of these systems. For detailed procedures, refer to the Commodore VIC-20 Maintenance Guide.

PCB Schematics & Service Guide

The VIC-20 features a modular motherboard design, facilitating repairs and upgrades. Detailed schematics and service manuals are available within the Commodore VIC-20 Technical Manual. Notable assembly versions include:

Assy 324003 – Early NTSC models.
Assy 251027-01 – VIC-20CR revision D (NTSC, new design).
Assy 324001-03 – VC-20 rev.B (PAL, old design).

Motherboard Images

Logic Board	Schematic Diagrams
Commodore VIC-20 Logic Board	VIC-20 Logic Board Schematic

Commodore VIC-20

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