Editing Commodore 64

{{Infobox computer
| name         = Commodore 64
| image        = [[File:Commodore64.jpg|250px]]
| caption      = Commodore 64 – the best-selling home computer
| manufacturer = Commodore Business Machines
| type         = Home computer
| release date = August 1982
| discontinued = April 1994
| 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 generator)
| storage      = Datasette cassette recorder; 1540/1541 5.25-inch floppy drive
| display      = 320×200 pixels, 40×25 text characters, 16 colours
| graphics     = MOS 6567 (NTSC) / 6569 (PAL) VIC-II, 8 hardware sprites
| sound        = MOS 6581 / 8580 SID: 3 voices, 4 waveforms, filter, ADSR
| dimensions   = 40.6 cm × 21.6 cm × 7.6 cm
| weight       = 1.8 kg
| power        = External brick: regulated +5 V DC and 9 V AC, 7-pin DIN
| os           = Commodore BASIC 2.0 in ROM
| predecessor  = [[Commodore VIC-20]]
| successor    = [[Commodore 64C]]
| codename     = VIC-40
| model        = C64, C64C, SX-64
| logo         = [[File:Commodore 64 logo-00.svg|250px]]
}}
<templatestyles src="Template:StyledTable/styles.css" />

The '''Commodore 64''' (C64) is an 8-bit home computer introduced by Commodore Business Machines in August 1982 and sold until Commodore's collapse in April 1994. It is generally regarded as the best-selling single computer model ever made; the commonly quoted range is '''12.5 to 17 million units''', the upper figure being Commodore's own claim and the lower an estimate derived from Commodore's published financial data. No audited production total was ever released, so any single number given as fact is a choice between those two.<ref name="reimer">Jeremy Reimer, "Total share: 30 years of personal computer market share figures", Ars Technica, 14 December 2005, and the author's subsequent sales-data spreadsheet. The source of the ~12.5 million estimate, derived from Commodore's quarterly reports, against Commodore's own marketing claim of 17 million.</ref>

'''The hardware figures on this page are taken from Commodore's own service literature''' — the ''C64 / C64C Service Manual'' and the ''Commodore 64 Technical Manual and Parts List'', both hosted here.<ref name="sm">Commodore Business Machines, ''C64 / C64C Service Manual'', March 1992, PN-314001-03, hosted at [[Commodore 64 / 64C Service Manual]]. Contains the board-identification tables, the circuit-theory sections describing the power supply, reset and clock circuits, component-level parts lists for every mainboard assembly, Commodore's symptom-to-component troubleshooting table, and schematics 252278 (B-3) and 252312 (E).</ref><ref name="tmpl">Commodore Business Machines, ''Commodore 64 Technical Manual and Parts List'', hosted at [[Commodore 64 Technical Manual and Parts List]]. Assembly-level parts lists and board drawings.</ref>

== Architecture and processor ==

The CPU is the '''MOS Technology 6510''', a 6502 core with an on-chip 6-bit I/O port at $0000/$0001 used to bank ROM, RAM and I/O in and out of the address space and to control the Datasette motor. It runs at '''1.023 MHz''' on NTSC machines and '''0.985 MHz''' on PAL machines, both derived from the video crystal rather than from a separate CPU oscillator.<ref name="sm" />

'''The 6510's +5 V supply is pin 6, not pin 40.''' Pin 40 is RESET and pin 21 is ground. This matters because probing pin 40 for a supply rail is a documented way to misdiagnose a healthy CPU, and because the 6502 in other machines is pinned differently.<ref name="sm" />

== Memory ==

* '''64 KB RAM''', of which 38,911 bytes are free to BASIC.
* '''20 KB ROM''': 8 KB BASIC 2.0, 8 KB KERNAL, 4 KB character generator holding two 2 KB sets.

Banking is done by the 6510's port lines together with the /GAME and /EXROM lines from the cartridge port, so a cartridge can replace BASIC, the KERNAL or both.

'''$C000–$CFFF is plain RAM.''' It is a 4 KB block that no ROM or I/O device overlays, which is why so much machine code lives there. It is not an I/O window, and pages that describe it as one are wrong.

== Display and graphics ==

Graphics come from the '''VIC-II''' — 6567 on NTSC machines, 6569 on PAL:

* 320×200 pixels, or 40 columns × 25 rows of text
* 16 colours
* 8 hardware sprites of 24×21 pixels with collision detection
* Smooth scrolling and raster interrupts

== Sound ==

The '''SID''' (Sound Interface Device), 6581 on earlier machines and 8580 on later ones, provides three independent voices with ADSR envelopes, four waveforms (triangle, sawtooth, pulse, noise), ring modulation, oscillator sync and a multi-mode filter.

'''SID audio output is pin 27.''' Pin 28 is Vdd — the 12 V supply — and pin 26 is the external audio input. Taking audio from pin 28 puts 12 V into whatever you connect, and is a mistake that appears on a number of modding guides.<ref name="sm" />

== Power ==

The C64's power comes from an external brick that supplies '''a regulated +5 V DC rail and a 9 V AC winding''' on a 7-pin DIN. Commodore's circuit theory is explicit that the 5 V from the brick feeds the logic directly — there is no second regulator on the board standing between the brick and the chips, which is why a brick that fails high takes the custom chips with it.<ref name="sm" />

{| class="wikitable styled-table" style="width:80%; text-align:left;"
|+'''Power connector CN7, 7-pin DIN'''
! Pin !! Function
|-
| 1, 2, 3 || Ground
|-
| 4 || Not connected on long boards; +5 V on the E board
|-
| 5 || +5 V DC, regulated, from the brick
|-
| 6, 7 || 9 V AC
|}

'''Pins 1 to 3 are all ground''', so measuring between pin 1 and pin 2 measures nothing. The 9 V AC also appears across '''user-port pins 10 and 11''', which is where it is normally taken from for expansions.<ref name="sm" />

On the board, 9 V AC is rectified and regulated to produce '''+12 V''' (VR1, an MC7812CT, feeding the VIC-II, the SID and the audio stages) and a second '''+5 V''' for the video and clock circuits (VR2, an MC7805CT), plus a '''+9 V unregulated''' rail for the cassette motor.<ref name="sm" />

For over-voltage protection see [[Commodore 64 Power-Supply Protector (C64 Saver)]]; for a modern replacement mainboard see [[C64 Reloaded MK2]].

== Input, output and expansion ==

* '''Cartridge expansion port''' — full address and data bus, plus /GAME and /EXROM
* '''User port''' — 6526 CIA#2 port B, plus the 9 V AC on pins 10 and 11
* '''Serial port''' — Commodore's own bus, for 1541 drives and printers
* '''Cassette port''' — Datasette
* '''Two control ports''' — Atari-style 9-pin, also used by paddles, mice and light pens
* '''RF and composite video''' — the video connector is 5-pin DIN on the original board and 8-pin on all later ones, which is the easiest way to tell an original board from a revision<ref name="sm" />

== Board revisions ==

Commodore's own identification table. The assembly number is silkscreened on the board; the case badge tells you nothing useful.<ref name="sm" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''C64 and C64C mainboard assemblies'''
! Version !! Commodore's identifying factor !! PCB assembly !! Schematic
|-
| Original || 5-pin video connector (CN5) || 326298-01 || 326106
|-
| A (CR) || 8-pin video connector || 250407-01 || 251138
|-
| B || 8-pin connector, reduced oscillator circuit || 250425 || 251469
|-
| B-2 || Reduced oscillator with component changes || 250441-01 || 251469
|-
| B-3 || Only two RAM chips, U9 and U10 || 250466-01 || 252278
|-
| E || BASIC and KERNAL combined into U4, new memory controller at U8 || 250469-01 || 252312
|}

'''250425 is a long board, not a C64C board.''' The two assemblies Commodore lists under C64C identification are the '''B-3 (250466-01)''' and the '''E (250469-01)''' — see [[Commodore 64C]].<ref name="sm" />

On the B-2, Commodore records that resistors R28, R29, R30, R36 and R48 were replaced by resistor pack RP5, and that diodes CR100–CR105 are no longer piggybacked but fitted at CR9 and CR12–CR16.<ref name="sm" />

=== Motherboard and schematic ===
{| class="wikitable styled-table" style="width:75%; text-align:center;"
|-
! Logic board !! Schematic diagrams
|-
| [[File:C64 Logic Board.jpg|thumb|center|350px|Commodore 64 logic board]]
| [[File:C64 Schematic Page 1.png|center|thumb|350x350px|C64 logic board schematic, page 1]][[File:C64 Schematic Page 2.png|center|thumb|352x352px|C64 logic board schematic, page 2]]
|}

== Maintenance ==

Failure modes worth knowing before opening one:

* '''The power supply.''' Potted in epoxy, not serviceable, and it gives no warning before it fails high. This is the single most destructive fault on the machine.
* '''Keyboard contacts.''' Carbon pads and a Mylar membrane, both of which wear.
* '''The regulators and the bridge rectifier.''' VR1, VR2 and CR4 are heavy-current, thermally cycled joints; a cracked one produces an intermittent that mimics a failing chip.
* '''The RF modulator.''' Degrades and is often bypassed rather than repaired.

For procedures see [[Commodore 64 General Maintenance]], [[Commodore 64 Troubleshooting Guide]] and [[Commodore 64 Capacitor Replacement Guide]].

== Documentation hosted here ==

* [[Commodore 64 / 64C Service Manual]]
* [[Commodore 64 Service Manual (1985 Mar)]], [[Commodore 64 Service Manual (1985 Feb)]] and [[Commodore 64 Service Manual (1985 Sep)]]
* [[Commodore 64 Technical Manual and Parts List]]
* [[Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01)]]
* [[Commodore Test Cartridge Index]]

== Gallery ==
<gallery mode="packed" heights="200">
File:Commodore-64-Computer-FL.jpg|Front view of the Commodore 64
File:Commodore-64-Computer-BL.jpg|Rear panel showing the I/O ports
File:Commodore 1530 Datasette C64.jpg|Commodore 1530 Datasette
File:C64 Logic Board.jpg|Internal motherboard layout
</gallery>

== Related pages ==
* [[Commodore 64C]]
* [[Commodore VIC-20]]
* [[Commodore 64 General Maintenance]]
* [[Commodore 64 Troubleshooting Guide]]
* [[Commodore 64 Capacitor Replacement Guide]]
* [[Commodore 64 Power-Supply Protector (C64 Saver)]]
* [[C64 Reloaded MK2]]

== References ==
<references />

[[Category:Commodore Systems]]