Commodore 64

Commodore 64
	Commodore 64 – The Best-Selling Home Computer
Specifications
Manufacturer	Commodore Business Machines
Type	Home Computer
Released	August 1982
Discontinued	April 1994
Intro price	US$595 (1982)
CPU	MOS Technology 6510 @ 1.023 MHz (NTSC) / 0.985 MHz (PAL)
Memory	64 KB RAM, 20 KB ROM (BASIC 2.0, KERNAL, Character ROM)
Storage	External cassette tape (Datasette), optional 5.25" floppy disk drive (1541)
Display	320×200 pixels, 40×25 text characters, 16 colors
Sound	SID 6581/8580: 3 voices, 4 waveforms, filters, ADSR envelope
Dimensions	40.6 cm × 21.6 cm × 7.6 cm
Weight	1.8 kg
OS / Firmware	Commodore BASIC 2.0 (in ROM)
Predecessor	Commodore VIC-20
Successor	Commodore 64C
Codename	VIC-40
Model no.	C64, C64C, SX-64

The Commodore 64 (C64) is an 8-bit home computer introduced by Commodore Business Machines in August 1982. With its advanced graphics and sound capabilities, it became the best-selling single personal computer model of all time, with estimates ranging from 12.5 to 17 million units sold.

🧠 Architecture and Processor

At its core, the C64 utilized the MOS Technology 6510 microprocessor, a variant of the 6502 with an integrated 6-bit I/O port used for memory banking and control of the Datasette. The CPU operated at:

1.023 MHz for NTSC systems.
0.985 MHz for PAL systems.

The 6510's integrated I/O port allowed for dynamic switching between ROM and RAM, enabling more flexible memory management.

💾 Memory and Storage

The C64 came equipped with:

64 KB RAM, with approximately 38 KB available for BASIC programs.
20 KB ROM, comprising:
- 8 KB for Commodore BASIC 2.0.
- 8 KB for the KERNAL (operating system routines).
- 4 KB for character ROM (two 2 KB character sets).

Storage options included:

Datasette – a cassette tape drive for loading and saving programs.
1541 floppy disk drive – a 5.25" drive offering faster and more reliable storage.

🖥️ Display and Graphics

Graphics were handled by the MOS Technology VIC-II chip, providing:

Resolution of 320×200 pixels.
Text display of 40 columns × 25 rows.
Support for 16 colors.
Hardware sprites: 8 sprites of 24×21 pixels, with collision detection.
Smooth scrolling and raster interrupts for advanced graphical effects.

The VIC-II's capabilities allowed for detailed graphics and animations, setting the C64 apart from its contemporaries.

🔊 Sound Capabilities

Audio was generated by the MOS Technology SID (Sound Interface Device) chip, offering:

3 independent voices with programmable ADSR envelopes.
4 waveform types: triangle, sawtooth, pulse, and noise.
Ring modulation and oscillator synchronization.
Programmable filters: low-pass, high-pass, band-pass, and notch.

The SID chip's rich sound capabilities contributed to the C64's popularity in music production and gaming.

🎮 Input/Output and Expansion

The C64 featured a variety of I/O ports:

Cartridge Expansion Port – for software cartridges and hardware expansions.
User Port – a versatile interface for modems, printers, and custom devices.
Serial Port – for connecting disk drives and printers.
Cassette Port – for the Datasette.
Two Joystick Ports – compatible with Atari-style controllers.
RF and Composite Video Outputs – for connection to TVs and monitors.

These ports allowed for extensive expandability, catering to both casual users and enthusiasts.

🧰 General Maintenance

Over time, Commodore 64 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 voltage regulators, potentially leading to 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 64 Maintenance Guide.

🧾 PCB Schematics & Service Guide

The C64 underwent several motherboard revisions, each with slight variations:

Assy 326298 – Early models with 8 RAM chips.
Assy 250407 – Common revision with improved reliability.
Assy 250425 – Featured in the C64C with consolidated chips.
Assy 250466 – Later C64C models with further integration.

📷 Motherboard Images

Logic Board	Schematic Diagrams
Commodore 64 Logic Board	C64 Logic Board Schematic (Page 1) C64 Logic Board Schematic (Page 2)

Commodore 64

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