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Commodore 64 - Technical Details

Data Sheet

  CPU         : 6510 @ 0.9852484444MHz [1] (PAL)
                       1.0227277143MHz [1] (NTSC)
  RAM         : 64kB DRAM
                .5kB SRAM (color RAM $d800-dbff)
  ROM         : 20kB ROM total, consisting of three ROMs
                (BASIC and Kernal share one ROM on new boards):
                  - 8k BASIC V2      ($a000-bfff)
		            - 8k Kernal        ($e000-ffff)
		            - 4k character ROM ($d000-dfff)
  Graphics    : VIC-II ($d000-d3ff)
  Sound       : SID ($d400-d7ff)
  Int. drives : -
  Interfaces  : 2 x control port (CIA #1 ($dc00-dcff)),
	              cassette port (CIA #1)
                  expansion port,
                  serial IEC (CIA #2 ($dd00-ddff)),
                user port (CIA #2)
  Keyboard    : 66 keys, controlled by CIA #1
  Power supply: external transformer (9VAC + 5V DC)
  Extras      : We don't need no frills ;-)

PCB History - Components - Documentation - Links

The different PCB versions (sorted chronologically)

1. Original

[Picture of original NTSC C64 board][Picture of original PAL C64 board]

Schematics: 158k GIF, 2897x2273 (Part 1), 131k GIF, 2669x2800 (Part 2)
Known revisions: ?

According to [2], this board has the PCB ASSY #326298-01; it can easily be recognized by its 5-pin video jack. The serial reset line is directly connected to the CPU so that you can use a serial reset button to reset the C64 (and all serial devices) [This is an assumption, because this is the case with the succeeding version A].

The following is an enumeration of features that all old boards (including #250441) have in common:

According to the board layout picture in [2], the PLA is on the left in U17 (beneath the CPU), while the SID is on the right in U18.

Please see below (Version B) for a discussion on the location of the SID and the PLA, before you start replacing them!

[ Help! Can you verify the PLA and SID locations? ]
[ Help! Can you verify that the CPU reset is directly connected to the serial reset? ]

2. Version A (CR)

[Picture of original C64 board]

[ Help! Schematics wanted! ]

Known revisions: REV.A, REV.B, REV.C

This board bears the PCB ASSY #250407 (or PCB ASSY #250407-04 according to [2]). It is the first C64 board using an 8-pin video jack, all newer boards use this connector. You can recognize this particular board by looking through the expansion port (viewing from behind, it is on the left side). If the rectifier bridge (it's in a black plastic case of 1x1cm) is BEHIND the fuseholder (which means that you might not be able to see it), then it's a version A (CR) board, if it is to the LEFT of the fuseholder, it's a version B board (or newer?).
Please see below (Version B) for a discussion on the location of the SID and the PLA, before you start replacing them!

[ Help! What is the difference between version A and CR or ACR? ]

3. Version B

[Picture of C64 Rev B board]
[ Help! Schematics wanted! ]

Known Revisions: ?

The PCB ASSY #250425 is not the only thing in which this board differs from the others. First of all, it has a reduced oscillator circuit; the numerous TTL chips providing both DOT and color clock have been replaced by a single clock generator IC (MOS 8701). Then the VIC-II's alignment has been changed from vertical to horizontal, so that pin 1 is in the lower left corner. Furthermore, the locations of SID (U18) and PLA (U17) have been SWAPPED, at least with respect to Version A (CR), so that the SID now resides near the upper edge of the board and the PLA an inch below. So VERY CAREFULLY check where to put SID and PLA if you want to replace them or swap them with chips from another board! The SID has to be placed into U18 and the PLA into U17.
Additionally to changing the color RAM's location (U6), Commodore also changed the location of the rectifier bridge (CR4), by which you can easily tell this version from version A (CR) (see Version A above).
In some revisions, the resistors R29 and R30 have piggybacked diodes, which seem to be protecting two lines of the serial port [?].

[ Help! What is the revision of the 'piggyback' boards? ]

4. Version B-2

[ Help! Picture wanted! ]
[ Help! Schematics wanted! ]

Known Revisions: ?

I haven't seen this board yet - actually I'm too lazy to open all my C64s to check for this board :-) All I know is that it has the PCB ASSY #250441-01. [2] states:

 All circuits remain the same as the 64B (Schematic 251469)
 with a few component location changes: 
    1) Resistors 28, 29, 30, 36, 48 were reduced to Resistor
       Pack RP5.
    2) Diodes CR100-105 are no longer piggybacked. Their new
       locations are CR9, 12-16.
Please see above (Version B) for a discussion on the location of the SID and the PLA, before you start replacing them!

[ Help! How can you tell this version from prior versions without opening the case? ]

5. Version ???

[Picture of C64 Rev B board]
(apologies for the picture, I had to paste it together from two sources)

[ Help! Schematics wanted! ]

Known Revisions: A

Someone donated a C64 with this board on 98/2/13. It has the PCB ASSY #250466-01. The most obvious difference to the previous boards is that it is the first board to use two 64kx4 DRAM chips, like in the new boards.
Please see above (Version B) for a discussion on the location of the SID and the PLA, before you start replacing them!

6. Version ???

6.1 REV.3 and REV.4
[Picture of new, short C64 board, Rev A

Schematics: 235k GIF, 3453x3009 (this diagram has been corrected quite a lot, but possibly still has errors. If you find them before we do, mail me!)
Known Revisions: REV.3, REV.4, REV.B

This is the first version of the totally redesigned boards, which were first employed in the C64G in 1987. It has the PCB ASSY #250469, REV.3 and along with the following boards, it will be referenced as 'short board'. The 64'er stated that this version has no 9VAC at the user port [3] ('ALDI' version, see notes at the end of this section). I have a board of the same revision and one of REV.4, and both of them do have 9VAC at the user port.
The easiest way to describe this board is to state that the location of the ports hasn't changed. :-) Ok, let's enumerate the major changes of this version:

As a result, the short boards are slightly incompatible [?]; e.g. SMON's TRACE command is said to malfunction. If anyone knows more about these incompatibilities, please mail me!

6.2 REV.B
[Picture of new, short C64 board with color RAM in MMU, 35k JPEG][Picture of new, short C64 board, Rev B

[ Help! Schematics wanted! ]

The main difference of REV.B, which was introduced in the end of 1990 [?], from REV.3/4 is that the color RAM is now in the MMU. This means that if the color RAM is damaged, you would have to exchange the MMU, which is not very easy, since it has a very narrow raster and 64 pins. Additionally, Commodore decided to protect CIA #1 by replacing the capacitors EM1-EM9 with strange looking capacitor/resistor combinations, the capacitors of which are said to break down easily and pull the appropriate input to GND.

Recognizing these new generation boards is easy: Look through the user port; if you can see two big chips sitting next to each other (the two CIAs), it's an old board, otherwise, it's a new, short board.

[ Help! What is the NAME of this version? Version C maybe? ]

Additional Notes

Component Locations

(Click here for ASCII version)

Old boards New boards
Original #250407 #250425 #250441 #250466 #250469R4 #250469RB
4066 (paddles) ? U28 ? U28 U18
4066 (ColorRAM) ? U16 ? U16 U21
556 ? U20 ? U20 -
7406 ? U8 ? U8 U22
BASIC ROM ? U3 ? U3 U4 (incl. Kernal)
Character ROM ? U5 ? U5 U5
CIA #1 ($dc00) U1 ? U1
CIA #2 ($dd00) U2 ? U2
Color RAM ? U6 ? U6 U19 -
CPU U7 ? U7 U6
DRAM ? U9-12
? U9-U10 U10-11
Kernal ROM ? U4 ? U4 U4 (incl. BASIC)
MMU - ? - U8
PLA U17 ? U17 -
SID U18 ? U18 U9
VIC-II ? U19 ? U19 U7

Note: Locations have been verified with MY board revisions (except for the original board, these are only conclusions!). If your board differs in component location, please mail me!

[ Help! Can you fill out the rest? Please VERIFY locations on your board first! ]


Related Links

[1] 64 intern, Data Becker 1983, pp.303-306
[2] Commodore 64 Service Manual
[3] 64'er 7/92, p.22
[4] Oliver Paul reported that

Updated: June 20, 2009
Created: September 1st, 1997
Status : Verified on September 9th, 1997
Thanks to:

Site copyright © 1997 by Marc-Jano Knopp
This document is part of MJK's Commodore 64 & LCD Page
Brought back to life by Peter Schepers, Dec 10, 2005 because I really liked this site!