Notes from Patrick Linstruth:

These are the firmware source listings for the original DJ2D (I call it the Model A) and the Model B.

I could not find any actual firmware files for the model A. It looks like it wasn't distributed on the CP/M 1.4 disks.

I got a copy of Tim's PROM, disassembled it, and then added all the labels and comments from the source listing in the manual.

Tim's has a small patch that doesn't appear in the source listing. The patch also doesn't appear in the Model B source listing during its SLOOP processing. The patch toggles the AENBL bit when flipping the density bit while trying to determine a disk's density. AENBL controls whether or not PREADY is brought low until the 1791 raises the DRQ line. I think this is similar to WAIT register on the Tarbell, so the CPU stops until the next byte of data is available. I'm not sure why they toggle that in the patch, since I don't think it has any impact during a VERIFY command. Maybe you can figure it out. Search for APATCH.

FIRMA.ASM is the source as it appears in the documentation's source listing.
FIRMAP.ASM has the "patch" from Tim's PROM.
FIRMB.ASM is the source as provided on the CP/M 2.2 disks for the Model B.