PROJECT TESTED - WORKING FINE ON MY 1977 COMMODORE PET

Drop-in replacement for the nowadays impossible to find 6540 ROM chipset used in the early versions of the Commodore PET 2001 using a 2716 or 2732 EPROM.

Instructions (see the pictures to better understand):

1) put the 74HCT138 on the component side and solder it from the solder side

2) put the two 14 pin headers on the solder side and solder them from the component side - Tip: put the headers into a breadboard or into the 24 pin socket you will solder at point #3 in order to keep them perfectly vertical and preserve the correct alignment, that will be very important when you will try to put the adapter into the PET sockets. Due to lack of space, if the headers aren't 90° aligned respect the PCB, the adapters will not fit side by side.

3) Put the 24 pin socket on the component side and solder it from the solder side

4) Put the 100 nF ceramic capacitor from the component side and solder it from the solder side

5) Program the EPROM using the given images (see below). You can also find them on zimmers.net - NOTE: 02.bin is for 2716 EPROM. 02-8k.bin is for 2732 EPROM and so on.

6) Put the EPROM in the adapter socket ; put the adapter in the Commodore PET socket. NOTE: if possible, replace one ROM at once and test it with some software (a quite picky program is INVADERS for PET; I use it for a fast test).

NOTE: the adapter will work as drop-in replacement for all the ROM chips, including the characters ROM.