What is it?

This is a board which plugs into the 6502 CPU socket on a Commodore PET computer to replace the main system ROM or RAM.

It is compatible with the following machines

• 9" PET - 2001, 2001N, 3008, 3016, 3032, 4008, 4016, 4032
• 12" PET/CBM - 4016, 4032, 8032, 8032-SK

It can be used on CBM 8096 and 8096-SK, but the 64K board cannot be used, so it will revert to an 8032. It cannot be used on the CBM 8296 or any CBM-II series machines.

The video RAM and character ROM are not replaced as they are wired directly to the video circuitry. I have replacement boards for those, see elsewhere in my store.

Why did you make it?

ROM and RAM failures are the most common fault on Commodore PET machines. The chips are difficult to find replacements for these days, especially when you have to find up to 16 RAM chips and 7 ROM chips.

This board can also be used to expand the memory of an 8K or 16K PET to the full 32K, and to replace BASIC 1.0 or 2.0 with the latest BASIC 4.0.

With this board installed, you are encouraged to remove all the socketed ROM and RAM chips to improve reliability and reduce power consumption and therefore heat generation inside the case. Any still working chips should safely stored away.

What makes it special?

The DIP switches can be used to turn on or off ROM and RAM replacement, and also to select the ROM set. There are 8 ROM sets, 4 of which are for the 9" PETs without CRTC chips

• A simple RAM / character set tester
• BASIC 1.0
• BASIC 2.0
• BASIC 4.0

The other 4 ROM sets are for 12" PET / CBM models with 6545 CRTC

• 40 column, normal keyboard, 50Hz
• 40 column, normal keyboard, 60Hz
• 80 column, business keyboard, 50Hz
• 80 column, business keyboard, 60Hz

The BASIC 2.0 and 4.0 ROM sets all include a DOS wedge to make accessing an IEEE-488 disk drive easier. BASIC 1.0 does not support IEEE-488 disk drives.

Only a 6502 CPU should be plugged into the socket on the ROM RAM board. 64K RAM boards, 6509 boards from the Super PET or other extensions are not supported.

There are two versions available.

• The smaller 5 switch version is ideal as a fit and forget upgrade to the maximum RAM and latest ROMs.
• The larger 9 switch versions allows you to control which banks of RAM and ROM are replaced, allowing you to diagnose faults. But otherwise is the same as the smaller version.

More info on my blog:

http://blog.tynemouthsoftware.co.uk/2016/09/commodore-pet-rom-ram-boards.html