NOTE: Please note that everything provided here is as is. I didn't test or read extensively that material. Discretion is advised.
All those files were found on the internet, don't exactly remember the sources.
| Firmware Version | Model | Firmware Level | File | Source |
|---|---|---|---|---|
| P221B | Unspecified | -1 (Version 1) | p221b.zip | Don't remember |
| P221B12 (P221M?) | BX? | -1 (Version 1)¹ | p221b12.zip | Don't remember |
| P231C[70905A](1997) | Unspecified | -2 (Version 2)² | p231c.zip | Don't remember |
| P231C | Unspecified | -2 (Version 2)² | p231c_olddos.zip | Old-DOS.ru |
| P271A | Unspecified | -6 (V6) ?³ | p271a.zip | Don't remember |
| P271C | Unspecified | -6 (V6) ?³ | p271c.zip | Don't remember |
| P271D | B? | -6 (V6) ?³ | p271d.zip | Don't remember |
| P271F | Unspecified | -6 (V6) ?³ | p271f.zip | Don't remember |
| P271H | Unspecified | -6 (V6) ?³ | p271h.zip | Don't remember |
| P271I | Unspecified | -6 (V6) ?³ | p271i.zip | Don't remember |
1: According to this thread, B12M is described as «with P222B12M special downgrade version for 12MHz CPU, for tandem configuration only» (Firefox translation.)
2: From the same thread, we learn P231B is «the latest version for some old motherboards with 256K RAM», which seems to suggest that release requires 1 MB RAM installed.
3: I wasn't able to find solid information for P271x releases, thus far… One would assume they're newer, but the aforementioned thread shows P211x from -4 onwards, so I can't tell for sure, however, several threads mentions it as a fairly new thing, using 4.0x programming software, which is one of the newer ones, that thread also goes into more detail, but since it supports PRI, I'm going to assume it's -6 (Version 6) level.