I was reading my copy of EXTEND YOUR HP-41 by W Mier-Jedrzejowicz, pages 639-642, ROM Revisions . I wanted to check the ROM revisions on my HP-41's.
The HP-41 is a 64K computer, divide into 16 4K pages of ROM. The most significant digit of the 4-digit hexadecimal address is the page, i.e., the system ROM's begin at adresseses 0000, 1000 and 2000. The TIME module begins at 5000, the printer at 6000, the HP-IL at 7000. The lower and upper ports start at 8000 (lower Port 1) through F000 (upper port 4).
The ROM revision letter is a single letter located at xFFE in each ROM where x corresponds to the page 0 through F.
One way to check this is the following:
1. Assign STO b to a key. The PPC ROM function MK works. Use 145, 124, -12 to assign it to the shifted B key.
2. create the nonnormalized number 00000000xFFD, where x is the RO<M page of interest (0, 1 or 2 for system ROMs).
3. Go to any program in any ROM, for example if MATH pac is installed GTO "SINH".
4. Press key where STO b is assigned.
5. Press SST and keep it down. You should see the next program step. LBL 00 corresponds to a revision A, LBL 01 to revision B, and so on to LBL 14 which corresponds to O.
Here are the System ROM versions for ROM pages 0, 1 and 2:
ROM's Date Codes Comments
----- ---------- ----------------------
DDE 1926-1940 All classical bugs
FDE 1936-1952 Bug 3 removed
FEE 1951-2034 Bug 1. 2. 4 removed as well
GFF 2035-84?? Bug 5, 7, 8 removed too. The first version of the H-41CV
HFF 84??-present The current versionm of the HP-41CX
NFL 2329-present Current version of the HP-41CX
Again from page 632 Revision numbers are not always changed, even when small changes are made to the instructions in a ROM. The HP-41CX revision numbers have not been changed, though a number of changes have been made to the reset code (what happens when you press ON while holding down ENTER and backarrow). Even the change in the turn-on code which makes it possible to do a MEMORY LOST when you have a zero length buffer did not merit a new revision number.
My Question - finally
How can I tell which version of HP-41CX I have, since the revision letters have not changes? Are there more that two releases of HP-41CX operating systems? Does anyone else care? Tools I have to look at ROMs are CCD Module, PPC ROM, ZENROM, HEPAX Module, and others.
Best Wishes,
Chris