reprom64

replacement rom adapter for the commodore 64

Reprom64 Rev.3

This is a rom adapter board for the C64 which replaces all rom chips with a single 64kb 27C512 Eprom, offering space for four different kernals, four charsets and two basic roms. Any combination of roms can be chosen using control lines provided on the board. A GAL16V8 decodes the chip select signals from the board and addresses the eprom accordingly.

Documentation is available in both english and german.

As far as the C64 rom chips are concerned, there a two different basic types of mainboards: the older revisions (up to and including 250466) use three separate 24-pin rom chips layed out next to each other. The newer revisions (250469) combine kernal and basic rom in a single 28-pin rom next to the charset rom.

This is a single board layout that can be used for all c64 mainboard types. By soldering in pin headers and jumper wires in different locations, the resulting build will be usable in either old or new boards. In old boards, the adaptor will sit in the kernal socket, and plug into the basic and charset sockets to the left and right for the chip select signals. In new boards, the adaptor will sit in the combined kernal and basic socket, and only plug into the charset socket to the left.

Downloads

Source

The source distribution includes the source for the 16V8GAL logic as well as schematics and pcb layouts in KiCad format.

Latest stable is reprom64-1.3.tar.gz.

All releases can be found under /download/reprom64

Latest developments are available via github:

git clone https://github.com/hbekel/reprom64

Binaries

Ordering Assembly Kits

I’m offering assembly kits including the reprom64 pcb, the preprogrammed GAL and all required components (except connection cables or switches) for 10€ each (without eprom) or 11,50€ (with eprom). Worldwide shipping via airmail is free of charge.

You can order kits via email at h.bekel@googlemail.com

To place an order, please include the word “reprom64” in your subject. State your full name, the number of kits you want and your complete international shipping address. You will then receive an email containing payment information (bank transfer only).

Please note that you will have to pay in advance to confirm your order. Since I’m doing all of this in my spare time and on a short budget, I can’t afford to keep complete assembly kits on stock. Instead, I will keep just the PCBs in stock and buy the remaining parts when a sufficient number of orders is reached. This means that it could take a few weeks until you get your kits. However, I will inform you about the status of your order in regular intervals.

Assembly

Depending on the mainboard type, pin headers and jumper wires have to be soldered at different positions. Please select your board type from the checkbox below:

IC Adapter strips down to sockets
Jumper wires (bridges)

The pin headers are soldered from the top. All other parts are soldered from the bottom side.

It is recommended to first insert all the pin headers into the mainboard sockets and then put the adpater board on top to solder the first few pins. This will ensure that the board will fit nicely into the sockets regardless of possible small variations in socket and pin header spacing.

Please note that adress bus signals A5 and A8 available on the right side of the board do not have to be connected at all for the proper operation of the Reprom64. They are provided simply as a convenient place to access these signal in case you want to install other hardware that needs them. For example, stereo SID adapter boards typically need access to A5 and A8.

List of parts

Reference Type Value Package/RM
C1 Ceramic capacitor 100nF 2.5mm
C2 Ceramic capacitor 100nf 2.5mm
U1 27C512 + Socket 64kb DIP-28
U2 GAL16V8D-15LP + Socket - DIP-20
P1 Precision Pin Header straight 40pin 2.5mm
P2 P3 P4 Pin header angled 2pin 2.5mm

Eprom Layout & Control

The table below shows the eprom layout and the corresponding control line states. The control lines are available at the pin headers labeled BASIC, CHARSET and KERNAL, where bit 1 is available at the left pin and bit 0 is available at the right pin, except for the Basic pin header which provides bit 0 at both pins.

The control lines are pulled high by the internal pullup resistor of the 16V8GAL. Thus simple SPST switches to ground can be used to select the desired ROM. If left open or unconnected, the line is driven high (1), if closed, the line is driven low (0).

Address Range ROM K1 K0 C1 C0 B0
f000-ffff Charset 3     1 1  
e000-f000 Charset 2     1 0  
d000-e000 Charset 1     0 1  
c000-d000 Charset 0     0 0  
a000-c000 Basic 1         1
8000-a000 Basic 0         0
6000-8000 Kernal 3 1 1      
4000-6000 Kernal 2 1 0      
2000-4000 Kernal 1 0 1      
0000-2000 Kernal 0 0 0      

License

                   reprom64 Hardware and Firmware
     Copyright (c) 2015, Henning Bekel <h.bekel@googlemail.com>

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