HP-41 ROM Versions / Bugs

All bugs are described in detail in the book „Extend your HP-41“ by W. A. C. Mier-Jędrzejowicz.

HP-41 Bugs

#1Early machines did not save X into L when Σ+ and Σ- were done.
Example: 41 Σ+ LastX, if you do not see 41 bug is present.
PPC Journal V6N5P27
#2Early machines allowed RCL IND nn and STO IND nn when nn was outside the memory range.
Example: Master Clear, SIZE 000, 999, ENTER, π, STO IND Y, CLST, 999, RCL IND X. If π is displayed, bug is present and the question is where is it being stored if the machine doesn’t have any data registers?
PPC Journal V6N5P28
#3Early machines allowed SF,CF,FS?C, and FC?C IND nn with nn any number (but not a stack register) 0 to 55.
Example: 49, STO OO, SF IND 00. If you see the BAT indicator bug is present.
PPC Journal V6N5P28
#4Early models compute the SIN of small angles incorrectly.
Example: 1 EEX CHS 99 SIN. If the result is 0.174532925 bug is present.
PPC Journal V6N6P30
#5CLP would only clear 1089 program lines.
#6-67A/-97A programs that contain combinations of number entry, EEX, and CHS do not translate correctly.
Example: EEX CHS 7 CHS 5 translates to E-7-5 instead of 1E-7 -5.
#7The second nybble of the seventh byte of Alpha is copied along with the first six bytes during an ASTO.
#8Early machines do not decompile programs if they are turned off during PRGM mode.
#9Executing CAT 1 while in PRGM mode, then interrupting it with R/S causes step labelling oddities.
#10If flag 25 is set and MEAN or SDEV causes an overflow, some flags can be altered.
#11If a program at the end of CAT 1 is replaced or deleted, a return to that program will return into the new program or off-program memory.
#12On early models, the function LN(1+X) gives wrong answers for values of X between -.9990234374 and -1.00.
#13On early models, the operation (.1)^-43 gives an answer of 9.999999999E42 instead of 1E43.
Table 1: HP-41 Bugs

HP-41 ROM Versions

VersionDate CodesComments
DDDsee here
DDE1926-1940all bugs
FDE1936-1952#3 removed
FEE1951-2034#1,#2,#4 removed
GFF2035-84??#5,#7,#8 removed
first -41CV version
HFF84??-presentcurrent -41CV version
NFL2329-presentcurrent -41CX version
Table 2: HP-41 ROM Versions

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