MPS 6540 Commodore PET 2001 ROM Adapter (Obsolete Rev. 3 Version)

This adapter allows you to replace a type MPS 6540 ROM in a Commodore PET 2001 with a standard 2716 EPROM.



I have been selling ROM adapters for the Commodore PET-2001 since 2009. Over these last five years I have been honing my design skills on my many different replacement electronic parts and through that process I have realized that my adapters are much in need of an update, so here it is. (If for some reason, you would like to buy the old version, it is still for sale here.) This new generation of ROM has many improvements including:

-A 74HCT138 decoder IC instead of the primitive diode-transistor logic used in the first version. This means a more reliable replacement that more accuratly mimics the original MPS6540.
-The clock signal is now wired as an additional ‘chip-select’ line to more closly mimic the behavior of the original MPS6540.
Batten and Allen PCB edge pins instead of round wire pins. The old adapters would only work reliably in one of the two types of DIP socket used in the original PET. These new pins exactly replicate the shape of a proper DIP pin and thus will work reliably in any DIP socket without damage. No kind of through-hole pin can claim this!
-An overall lighter weight and shorter design. This means that that part will be less likely to come loose from the socket if the PET is jarred.

You will receive:
– One adapter capable of replacing a single MOS Technologies MPS6540 ROM chip.
– The needed 2716 ROM chip, programmed with the code you need. Please specify the full part number of the original chip when ordering so that I can program the replacement correctly.
– A lifetime guarantee on the adapter. If the adapter does not work in your computer I will work with you until the problem is solved. If the adapter ever fails, just mail it back to me for a free repair.

PLEASE NOTE: These adapters will ONLY work to replace a chip with a part number starting with 6540. They will NOT replace types 2332, 2316, or other ROM types used in Commodore computers other than the original Commodore PET 2001. If you don’t know if you have a bad ROM chip, or if you don’t know which one is bad, you may be interested in my EPROM Programmer Universal Adapter which, when used in conjunction with an inexpensive Willem EPROM programmer, will allow you to read (and therefore test) an MPS6540 ROM chip. You can also read my guide to troubleshooting the Commodore PET 2001 here.

These adapters replace MOS Technologies proprietary ROM chips with standard 2716 ROM chips and have the following features. They:
1) Are pin-compatible electrical replacements for the mps6540 (except that they do not require a clock signal.) All five chip select lines are fully functional.
2) Have a small enough footprint that the adapters can replace any or all of the ROM chips in a PET 2001.
3) Use only vintage-style through-hole parts so they will not look out of place in a 1977 PET.

The one disadvantage of these adapters is that with a 2716 inserted they are about 0.3″ taller than the original 6540 chip and thus may not be mechanically compatible with all 3rd party expansion boards. Please make the appropriate measurements before ordering.

Download the schematic and PCB layout for this product hereNote that these files are available for PERSONAL, NON-COMMERCIAL USE ONLY. In short, you are welcome to use them to build this product yourself, but you must contact me to work out a commission if you wish to sell anything derived from them. This product was designed in ExpressPCB so you will need to download a copy of that software from before you can view the files.


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