PET 2001 Emulator: Option ROMs

Just to let you know, in case you were interested…

A very brief update notice: Inching forward on the quest for feature creep, the PET 2001 emulator now supports ROM installation per drag&drop! See the description for details.

To add a bit of meat to this post, here are the ROM socket designators of the PET 2001:

• H1 … C000–C7FF
• H2 … D000–D7FF
• H3 … E000–E7FF
• H4 … F000–F7FF
• H5 … C800–CFFF
• H6 … D800–DFFF
• H7 … F800–FFFF

There are no sockets for option ROMs on the boards of the original PET 2001s.
Moreover, as there is no socket for B000–BFFF, we’re out of luck regarding BASIC 4 and restricted to the old and new ROM versions of Commodore BASIC. (Of course, we can always directly access the address bus on the CPU and thus provide for extra ROMs, but on an unmodified machine we are restricted in our firmware options.) Notably, the sockets, there are, are for 2K ROMs, while later models featured sockets for 4K ROMs.

On the PET 2001N, the one with the “real” keyboard, and CBMs, there are sockets for the full complement, including D3 and D4 for option ROMs:

• D3 … 9000–9FFF
• D4 … A000–AFFF
• D5 … B000–BFFF
• D6 … C000–CFFF
• D7 … D000–DFFF
• D8 … E000–EFFF *
• D9 … F000–FFFF

Finally, later PETs featured the following ROM socket designators:

• UD6 … F000–FFFF
• UD7 … E000–EFFF *
• UD8 … D000–DFFF
• UD9 … C000–CFFF
• UD10 (UD5) … B000–BFFF
• UD11 (UD4) … A000–AFFF
• UD12 (UD3) … 9000–9FFF

*) reserved I/O space at E800–EFFF.

Fun fact:
In the handwritten schematics, ”D800” for H6 looks much like “0800” and “B000” for D5 much like “8000”.