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Commodore 64

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Revision as of 09:40, 1 October 2026 by Josh (talk | contribs) (Rewrite: cite 1992 service manual page by page; add history (Ars, BCS), I/O map and port tables; SID VDD is 9 V on 8580 boards; drop uncited dimensions, weight, VIC-40 codename, sales range; remove bold and self-reference)
Commodore 64
Commodore 64 in the original case
Specifications
ManufacturerCommodore Business Machines
TypeHome computer
Released1982[1]
Discontinued1994[2]
Intro priceUS$595 (1982)[1]
CPUMOS 6510 at 1.02 MHz (NTSC), 0.985 MHz (PAL)
Memory64 KB RAM; 20 KB ROM
Storage1530 Datasette; 1541 floppy disk drive
Display320 × 200 pixels; 40 × 25 text; 16 colours
Sound6581 SID (8580 on late boards)
GraphicsVIC-II: 6567 (NTSC), 6569 (PAL)
PowerExternal supply: +5 V DC and 9 V AC on a 7-pin DIN
OS / FirmwareCommodore BASIC 2.0 and KERNAL in ROM
PredecessorCommodore VIC-20
SuccessorCommodore 128
Model no.C64; later Commodore 64C

The Commodore 64 (C64) is an 8-bit home computer made by Commodore Business Machines. It went on sale in 1982 at US$595 and has 64 KB of RAM, the VIC-II video chip and the SID sound chip.[1][3] It was built on six main board designs over its life, the last of them in the slimmer Commodore 64C case.

History

Commodore sold 2 million C64s in 1983. Annual sales were still 1.25 million in 1989 and fell to 175,000 in 1993.[1] Commodore never published a production total. The C64-Wiki gives 17 million as the most likely figure;[4] David Pleasance, Commodore UK's former managing director, said in 2019 that the figures he saw during a management buyout attempt put it "just a tad under 27 million".[2] Commodore International went into liquidation in April 1994.[2]

Variants listed by the C64-Wiki include the SX-64 portable (1983), the C64C in a flatter case (1986), the low-cost C64G (1988) and the keyboardless C64 Games System (1990).[4]

Processor and memory

The CPU is the 6510 (U7), a 6502-compatible processor with a six-bit I/O port, P0-P5, controlled through locations $0000 and $0001. The port switches the ROMs in and out of the address map and drives the cassette interface: P3 is the write line, P4 senses the play key and P5 switches the motor.[5][6] Commodore lists a 1.02 MHz clock.[3] The VIC-II divides the dot clock (8.18 MHz NTSC, 7.88 MHz PAL) by eight to make the CPU's phase 0 clock.[7]

The 6510's +5 V supply is pin 6 and ground is pin 21; pin 40 is RESET.[5]

The 64 KB of RAM is eight 4164 DRAMs on the long boards, with a 2114 static RAM (U6) holding the 1 K × 4-bit colour memory.[8] The B-3 and E boards use two 64K × 4 DRAMs.[9] BASIC has 38,911 bytes free at power-up.[4]

The 20 KB of ROM holds BASIC at $A000-$BFFF, the KERNAL at $E000-$FFFF and the character generator, which the processor sees at $D000-$DFFF when I/O is switched out. The PLA (U17, an 82S100 on the long boards) decodes the ROMs, the I/O chips and the cartridge lines ROML ($8000-$9FFF) and ROMH.[10] The 6510 port lines and the cartridge's GAME and EXROM lines together select the memory map. The block at $C000-$CFFF is RAM in every configuration except the cartridge "Ultimax" mode, in which it is unmapped.[11]

I/O addresses decoded by the PLA[10]
Device Address range
VIC-II $D000-$D02E
SID $D400-$D7FF
Colour RAM $D800-$DBFF
CIA 1 (U1) $DC00-$DC0F
CIA 2 (U2) $DD00-$DD0F
I/O 1 (expansion port) $DE00-$DEFF
I/O 2 (expansion port) $DF00-$DFFF

Video and sound

The VIC-II is a 6567 on NTSC boards and a 6569 on PAL boards.[12] Commodore's specification gives 40 columns × 25 lines of text, 16 colours, 320 × 200 pixel bitmap graphics and eight sprites of 24 × 21 pixels, each with up to four colours, independently expandable, with sprite-to-sprite and sprite-to-data collision detection.[3]

The 6581 SID has three tone generators covering nine octaves, each with an ADSR envelope and sawtooth, triangle, variable pulse and noise waveforms, plus low-, high- and band-pass filtering and an external audio input.[3] Its audio output is pin 27 and its audio input pin 26; the SID also reads the paddles on pins 23 and 24.[13] Pin 28 (VDD) takes the +12 V rail from VR1 on the long boards. On the E board it comes from a transistor regulator set by zener CR7: 12.6 V for a 6581, 9.6 V for the 8580.[14]

Power

The external supply (Commodore part 251053-02 in the US parts list) provides regulated +5 V DC and 9 V AC.[15][14] The +5 V passes through the power switch and supplies the logic directly; only the video and clock circuits take their +5 V from an on-board regulator.[14] A supply that fails with a high output therefore puts that voltage on the processor logic. The C64-Wiki records that the original supplies tend to rise in voltage as they age and that most C64s killed by their supply had seen more than 6 V, the RAM usually failing first.[16]

Power connector CN7 (7-pin DIN)[14]
Pin Long boards E board
1, 2, 3 Ground Ground
4 Not connected +5 V
5 +5 V DC +5 V DC
6, 7 9 V AC 9 V AC

The 9 V AC also appears on user port pins 10 and 11.[14] On the long boards it is used three ways: rectified by CR4 and regulated by VR2 (MC7805CT) to "+5 V CAN" for the video and clock circuits; combined with the rectified DC through CR5 and CR6 and regulated by VR1 (MC7812CT) to +12 V for the VIC-II, SID and audio stages; and left unregulated at about 9 V DC for the cassette motor.[14] The E board has neither regulator. The Commodore 64 Capacitor Replacement Guide and Commodore 64C Capacitor Replacement Guide describe each board's supply in detail. For an over-voltage cut-out see Commodore 64 Power-Supply Protector (C64 Saver).

Ports

External connectors
Port Connector Notes
Cartridge / expansion (CN6) 44-pin card edge Processor address, data and control bus; ROML, ROMH, I/O 1, I/O 2, GAME and EXROM[10]
User port (CN2) 24-pin card edge CIA 2 port B (PB0-PB7), the two CIA serial ports and their clocks, and 9 V AC on pins 10 and 11[17][14]
Serial bus (CN4) 6-pin DIN Commodore serial bus for the 1541 and printers, driven by CIA 2 PA3-PA7 through the 7406 (U8)[17]
Cassette (CN3) Card edge 1530 Datasette; write from 6510 P3, motor from P5, read to CIA 1 FLAG[6]
Control ports (CN8, CN9) 9-pin D Joysticks and paddles; paddles are read by the SID[13]
Audio/video (CN5) 5-pin DIN on the 326298 board; 8-pin DIN on later boards The 8-pin version adds separate luminance and colour outputs[18]
RF output RF modulator (M1) Composite video and audio modulated for a television[13]

Board revisions

The assembly number is printed on the board. Commodore's identification table:[9]

C64 and C64C board assemblies
Version Assembly Schematic Identifying factor (Commodore)
Original 326298-01 326106 5-pin video connector
A (CR) 250407 251138 8-pin video connector
B 250425 251469 8-pin; reduced oscillator circuit
B-2 250441-01 251469 As B, with component location changes
B-3 250466-01 252278 Two RAM chips, U9 and U10
E 250469 252312 BASIC and KERNAL combined in U4; new memory controller at U8

The first four are full-length "long boards". Commodore lists the B-3 and E under C64C identification.[9] On the B-2, resistors R28, R29, R30, R36 and R48 became resistor pack RP5, and diodes CR100-CR105 moved from piggyback positions to CR9 and CR12-CR16.[9]

Board and schematic

Logic board Schematic
250407 board, artwork 251137 rev. C
C64 schematic, sheet 1
C64 schematic, sheet 2

Maintenance and repair

Commodore's troubleshooting table starts with the external power supply for a blank screen at power-up and for bands that scroll through the picture as the machine warms up, before naming any chip.[19] Measure the supply's +5 V output before opening the case.

Documentation

Commodore

Document Contents
Commodore 64 / 64C Service Manual March 1992, PN-314001-03. Specifications, circuit theory, troubleshooting table, board identification, and parts lists, layouts and schematics for 326298, 250407, 250425, 250466 (B-3) and 250469 (E). The only hosted Commodore source for the B-3 and E boards.
Commodore 64 Service Manual (1985 Mar) and Commodore 64 Service Manual (1985 Sep) Earlier scans of the same manual, PN-314001-02, covering 326298, 250407 and 250425. Commodore 64 Service Manual (1985 Feb) holds the March file.
Commodore 64 Technical Manual and Parts List P/N 990439. Commodore's drawing packages for assemblies 250407 (rev. B) and 326298, with parts lists, layouts and schematics.
Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01) Commodore's dealer diagnostic cartridge and harness.
Commodore 64GS Technical Data (400401-01, 1990 May) The C64 Games System, assembly level only.
Commodore Test Cartridge Index Diagnostic cartridges.

Books

The wiki hosts many third-party C64 books; Category:Commodore Books is the annotated index. Most are programming books. Those that cover the hardware include Troubleshooting and Repairing your Commodore 64 (Art Margolis, TAB Books), Commodore 64 Troubleshooting and Repair Guide (Robert C. Brenner, Howard W. Sams), The Commodore 64 Kernal and Hardware Revealed (Nick Hampshire, Collins) and The Anatomy of a Commodore 64 (Data Becker). They are secondary to Commodore's manuals.

  • Commodore 64, front
    Commodore 64, front
  • Rear panel
    Rear panel
  • 1530 Datasette
    1530 Datasette
  • 250407 logic board
    250407 logic board

References

  1. ↑ 1.0 1.1 1.2 1.3 Jeremy Reimer, "Total share: 30 years of personal computer market share figures", Ars Technica, December 2005. Debut in late 1982 at US$595; 2 million sold in 1983; sales of 1.25 million in 1989 and 175,000 in 1993.
  2. ↑ 2.0 2.1 2.2 Martin Cooper, "The rise and fall of Commodore", BCS, The Chartered Institute for IT, 2 July 2019. Interview with David Pleasance, former managing director of Commodore UK.
  3. ↑ 3.0 3.1 3.2 3.3 Commodore Business Machines, Service Manual C64/C64C, March 1992, PN-314001-03, hosted at Commodore 64 / 64C Service Manual. Specifications, p. 1.
  4. ↑ 4.0 4.1 4.2 C64-Wiki, "C64". Retrieved 2026-10-01.
  5. ↑ 5.0 5.1 Service Manual C64/C64C (1992), pin assignments for U7 6510 and U17 PLA, p. 27.
  6. ↑ 6.0 6.1 Service Manual C64/C64C (1992), Circuit Theory, "The Cassette Interface Circuits", p. 11.
  7. ↑ Service Manual C64/C64C (1992), Circuit Theory, "The C64 Clock Circuits", p. 6; dot clock frequencies from the notes to schematic 252312, p. 42.
  8. ↑ Service Manual C64/C64C (1992), Circuit Theory, "RAM Control Logic", p. 8.
  9. ↑ 9.0 9.1 9.2 9.3 Service Manual C64/C64C (1992), "C64 Board Identification" and "C64C Board Identification", p. 17; parts lists pp. 34 and 40.
  10. ↑ 10.0 10.1 10.2 Service Manual C64/C64C (1992), Circuit Theory, "I/O and ROM Address Decoding and Expansion Port", p. 7.
  11. ↑ C64-Wiki, "Bank Switching". Retrieved 2026-10-01.
  12. ↑ Commodore, Commodore 64 Computer Technical Manual, P/N 990439, drawing 250407 rev. B, sheet 2 of 7 (PDF p. 5), hosted at Commodore 64 Technical Manual and Parts List.
  13. ↑ 13.0 13.1 13.2 Service Manual C64/C64C (1992), Circuit Theory, "8 Pin Video and Audio Output Circuits", p. 10.
  14. ↑ 14.0 14.1 14.2 14.3 14.4 14.5 14.6 Service Manual C64/C64C (1992), Circuit Theory, "The Power Supply", p. 4; notes 6 and 8 to E schematic 252312, p. 42.
  15. ↑ Service Manual C64/C64C (1992), Parts List, p. 2.
  16. ↑ C64-Wiki, "Power Supply", section "Failure". Retrieved 2026-10-01.
  17. ↑ 17.0 17.1 Service Manual C64/C64C (1992), Circuit Theory, "The Serial Interface and User Port Circuits", p. 13.
  18. ↑ Service Manual C64/C64C (1992), Circuit Theory, "5 Pin Video and Audio Output Circuits", p. 9, and "8 Pin Video and Audio Output Circuits", p. 10.
  19. ↑ Service Manual C64/C64C (1992), "64 Troubleshooting Guide", pp. 14-16.
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