C64 reloaded

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C64 reloaded (First Prototype)
C64 reloaded (Second Prototype)
C64 reloaded (final)

In 2014 the Commodore 64 celebrates it's 32nd birthday, and that's a significant birthday for a Computer: If written in hexadecimal notation, 32 becomes $20. To celebrate this, Individual Computers has prepared a limited production run of a new C-64 motherboard.

C64 Reloaded is available in limited quantity.



  • The schematics are close to Commodore Assy number 250466, because this version is accepted to be the best compromise between cost savings and compatibility. The circuit has been changed only in very few places, so production is still possible with parts that are available today.
  • C64 Reloaded fits in all original C64 cases: The classic "breadbox" cases and the flat versions of the case that were used in later production years. This includes the brand-new cases that were produced recently in a popular Kickstarter project.
  • Our new mainboard uses modern DC-DC converter technology: We recommend to use an EuP-compliant 12V DC wall power supply that will use less than 0.3W(*) in standby. The original C64 requires 3.9W(*) in standby, and when powered on, power consumption rises to 21.6W(*). Our C64 Reloaded only takes about 5,7 Watt(*) - roughly a quarter of what the original computer required, despite the fact that we're using the original Commodore chips. This economical approach doesn't mean "weak" in any way: The DC-DC converters have lots of power reserve to supply even very power-hungry expansions like the "Super CPU" or the Commodore memory expansions 1750 or 1764.
  • all required voltages (5VDC, 12VDC, 9VAC) are generated on board and are available at external interfaces as expected (tape, userport, expansion port, joystick port)
  • The C64 Reloaded does not come with a TV-Modulator. There's an S-Video output in it's place, which is located in place of the RF output.
  • Audio is passed to the outside world through a 3.5mm stereo plug, which lets you use standard audio equipment. It is located in place of the channel switch, so no additional holes must be drilled into the computer case. The second (left) channel is routed to a jumper pad for those who are using a stereo SID solution.
  • The known connectors for joysticks, cartridges, monitor, floppy drives, data cassette and userport are of course available on C64 Reloaded.
  • C64 Reloaded ships partly assembled. There are different versions of the board that include a varying number of original chips. A very small quantity has been fully equipped with all original, partly new-old-stock chips. The more cost-effective versions are equipped with used (partly scratched) CIA chips and have either empty ZIF-sockets, or replacement parts like the SuperPLA V3 or the CSG8701-replacement.
  • The CIAs, all RAMs, EPROM (for kernals, basic, chargen) are in precision sockets.
  • The processor (CPU), the sound chip (SID), the PLA and video chip are in zero-insertion-force sockets, so they can be exchanged easily. Those boards that are sold fully-equipped can be shipped without ZIF sockets at the choice of the customer.
  • As opposed to the original computer, our board can be jumpered between PAL and NTSC without the need to solder anything - the two required special-frequency crystals come preinstalled. This feature can only be used with a real 8701 timing generator chip.
  • proper 50/60Hz signal for the CIA TOD clocks is generated on board depending on selected video mode. The time base for this is another crystal oscillator, which is running independent of the main C64 clock circuit.
  • All ROMs are kept together in one 32k EPROM. The board can be equipped with two Kernal ROMs and two character ROMs. ROMs are properly licensed. The alternative Kernal and character ROM spaces in the EPROM are programmed with equal contents, so switching has no visible effect on boards that come fresh from the factory.
  • the power switch is a 3-position switch that has a "momentary" up-position, which is used to reset the machine. This gives you a reset-button without the need to drill a hole into a classic case.
  • pressing and holding RESTORE "long" (more than three seconds) will switch kernal ROMs.
  • holding RESTORE while resetting the machine will select an alternative character ROM.
  • Although we strive to replicate the C64 as close to the original as possible, we've introduced a technical innovation: A video effect known as "VSP-effect" to the C64 scene leads to intermittent crashes of some C64 models, which is also known as the "VSP-bug". All C64 Reloaded boards are equipped with the VSP-Fix. We've announced earlier that the VSP fix would be an option, but now decided to include it with all boards.
  • gold plated user- and tape ports
  • Comes including metal frame around the expansion port, like the original computer.
  • the final board is black with white silkscreen print

(*) Measured at the 230V AC side on an early prototype. Production boards take slightly more power. Measurement device not calibrated. Board equipped with 85xx HMOS chips

Power supply

Power supply available separately

The C64 Reloaded is shipped without a power supply. The power connector is a standard 12V DC plug, outer diameter 5.5mm, inner diameter 2.5mm. When selecting your power supply, please double-check the polarity: The inner conductor must be "plus"! The power supply should be able to provide at least 1 amp of current. 2 amps is recommended if you want to operate the C64 Reloaded with power-hungry devices like the Commodore 1750 or a SuperCPU. For best picture- and sound quality, the power supply should have less than 100mV ripple on 12V.

Operating the C64 on the supply of a car is not recommended. The voltage in a car is slightly too high and it would trigger the protection circuit of the C64 Reloaded.

If you have a spare power supply from an unused xDSL or cable modem, please double-check the technical data. Power supplies from Nequester and Fritz!Box are known to work.

Chip compatibility

The C64 Reloaded can be configured to use NMOS or HMOS chips in all combinations. While there is no need to do any changes if you swap CIA or CPU chips between NMOS and HMOS versions, the Video- and Sound chips require different voltages. Jumpers should only be altered when the computer is switched off and the DC plug has been removed.

CPU compatibility

The C64 Reloaded can work either with the 6510 or with the 8500 CPU. The CPU must be inserted with the notch facing towards the lever of the ZIF socket. There is no need to alter any jumpers - the chips are drop-in compatible. You can NOT use any other CPU (such as the 6502), because it is missing essential features (IO port and tri-state address bus).

CIA compatibility

You can use 6526 or 6526A CIA chips. These have minor differences in IRQ/NMI behaviour, but are mostly compatible with the majority of software.

SID voltage and filter selection

For the HMOS versions of the SID chip, namely 8580 and 6582, jumpers J6 and J3 must be open. Filter jumpers J4 and J5 must be closed. This will reduce SID voltage to 9V, and filter capacitors are set to 22nF. The C64 Reloaded is shipped in this configuration for safety reasons.

For the NMOS version of the SID chip - the 6581 - jumpers J6 and J3 must be closed, and filter jumpers J4 and J5 must be opened. This will give the SID 12V, and filter caps will be reduced to 470pF. CAUTION: A HMOS version of the SID will be destroyed if high voltage is applied!

VIC-II voltage selection

While the old versions of the VIC-II chip require 12V, the new HMOS version only requires 5V. Jumper J2 selects the voltage for the video chip: If the middle and left pins are connected, 12V is applied. If the middle and right pins are connected, the chip will get 5V. You normally don't have to alter this jumper at all, because the board comes configured according to the chip version that is installed.

VIC-II clock selection

The C64 requires a number of clock signals that are different depending on the video mode. These clocks always need to be chosen in accordance with the VIC-II chip version: PAL versions 6569 and 8565 require 17.7344MHz colour clock, and the TOD clock should be set to 50Hz. For NTSC versions 6567 and 8562, the colour clock must be 14.31818MHz, and the TOD clock should be set to 60Hz. These clocks are chosen with jumpers J7 and J8: Please refer to the pictures on the right for proper clock settings.

Note that J8 (colour clock selector) has no effect when the CSG8701-replacement circuit is used. The replacement circuit has it's own crystal, which should be chosen in accordance with the VIC-II type that you have installed. The replacement circuit will also not look at the J7 jumper setting, so J7 is reduced to only selecting 50Hz (closed) or 60Hz (open) TOD clock. This lets you simulate the timing of a PAL C64 operated on a 60Hz grid, or an NTSC C64 that is operated on a 50Hz grid.

PLA chip (U17)

The C64 Reloaded can work with any PLA revision that was used by Commodore (8700-based, 7700-based and 82S100-based), with CPLD-based replacement circuits such as SuperPLA V3 and RealPLA. Operation with an Eprom-based replacement circuit may cause permanent damage to the C64 Reloaded. Eprom-based replacement circuits may enable two components at the same time, causing bus contention. We'd like to express our apologies for mentioning such trivial information, but there are still people out there who think that Eprom-based logic replacements are a good idea.

Jumper pinouts

Jumper J13 signal names
header CN4b signal names
header J14

J13: additional SID support signals

The C64 Reloaded has an extra jumper for Stereo SID applications: J13 carries the required signals that a stereo-SID adapter may need to use:

Pin number Signal name
1 Sel_IOf (IO select for $df00)
2 (key pin; not installed)
3 Sel_IOe (IO select for $de00)
4 Audio_out 2
5 System Address line A5
6 Audio_out

The C64 Reloaded comes with a jumper placed over pins 4 and 6, so the 3.5mm stereo audio jack will provide an audio signal on both channels.

CN4b: auxilary IEC

This connector is not installed by default. The holes have been kept free of solder during production, so it's easy to install a pin header in this place. However, any soldering on the C64 Reloaded will void warranty! CN4b has not been installed for safety reasons: Since an installed header has no protection at all, the Vcc pin may be shorted, and up to 20W of power would lead to severe damage. We therefore recommend to only install this pin header if you know what you're doing, and if you're aware that your warranty will be void with this modification.

In addition to IEC signals, this port also carries a few datasette signals, which will give you access to valuable CPU IO port pins. Pin number 1 of CN4b is marked with a square pad. All other pads of this connector are round. The drill size used for the holes is 0.89mm.

Pin number Signal name
1 CASS_WRT (Datasette pin 5)
2 CASS_SENSE (Datasette pin 6)
3 Cassette motor control (CPU port pin P5, TTL-level)
5 VCC (caution: unfused!)
9 Reset
10 GND

J14: option select

Like CN4b, this connector is not installed by default. The holes have been kept free of solder during production, so it's easy to install a pin header in this place. However, any soldering on the C64 Reloaded will void warranty!

Pin number Signal name
2 Option select. Holding fire in joystick port 2 during reset will result in HIGH output.

alternative Kernal and character set

The C64 Reloaded allows installing and selecting an alternative Kernal and an alternative character set. To use this feature, you need to program your own EPROM with the new contents. The EPROM is a standard 27C256 type, and you should choose a 200ns or faster type. The memory map inside of the EPROM is:

Address range contents
$0000-$0fff first character set
$1000-$1fff second character set
$2000-$3fff Basic ROM
$4000-$5fff first Kernal ROM
$6000-$7fff second Kernal ROM

switching between Kernal ROMs

We believe that drilling a hole into a classic computer case is a bad thing - some people even call it sacrilege. The C64 Reloaded allows switching between two Kernal ROMs without the need to install a separate switch. After power-up, the first Kernal ROM is active. If you press and hold the RESTORE key for more than three seconds, the C64 Reloaded will switch to the other Kernal ROM upon release of the RESTORE key. The C64 Reloaded comes with both Kernal ROM spaces programmed with the same original Kernal ROM, so you will not see an effect of holding the RESTORE key unless you have exchanged the EPROM for your own one.

choosing an alternate character ROM

The C64 Reloaded normally starts with the first character ROM active. If you want to use the alternate character ROM (for example for a localized font), just hold the RESTORE key during reset: The state of the RESTORE key is sampled upon the release of the reset line, and the chosen character ROM will remain active until the next Reset. C64 Reloaded comes with both character ROM spaces programmed with the same original character set, so you will not see an alternate character set unless you have exchanged the EPROM for your own one.

using a larger EPROM for 4 ROM sets

You may use a 27C512 EPROM instead of the stock 27C256 EPROM to use 4 ROM sets instead of 2.

  • Burn the EPROM according to the above mentioned memory map, the second half of the EPROM should then follow the same layout as the first half.
  • Bend PIN1 so that it will not go into the socket, this is the highest address line (A15) of the 27C512 and thus can be used to select the first or second half of the EPROM.
  • If you do not want to add a switch, you may use the "option" pin 2 of J14. Then you can press and hold the fire button of joystick port 2 at reset time to select the second half of the EPROM.

Problems and Solutions

Mssiah Cartridge does not start

The Mssiah Cartridge seems to use an unusual protection against being dumped, which doesn't seem to work with the way the coldstart (poweron) reset is being generated on the C64reloaded board. You can work around this by using a userport reset button:

  • Power off the C64r, insert Mssiah cartridge
  • Press and hold the userport reset button
  • Power on the C64r
  • Release the userport reset button


We've created a public version of the C64 Reloaded schematics. Only a few components don't have values shown in the schematics. If you require assistance on how to get a switching regulator to work properly over a wide range of currents, or how to properly calculate the components of a crystal oscillator, so that it doesn't require adjustment and works in mass-production, we offer design consulting services.

Download: Media:C64_reloaded_pub_schem.pdf


  • Safe VSP - Demo that contains an in depth analysis and technical explanation of the "VSP-bug"
  • C64 Reloaded on c64-wiki (german)


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