WOODSTOCK Questions/Observations


I don't remember noticing this mentioned here before but I recently noticed some 'odd' behaviour on my HP25 (s/n 1603********).

An arithmetic operation that results in an overflow results in, as expected

' 9.9999999 99'

However when a register operation results in an arithmetic overflow then, rather than the expected error message,the calculator displays

' 0F          '

As my HP21 behaves in the same way I presume that this is intended, but as I don't have the manual I can't double check this. (I find it interesting is that unlike the normal error conditions the register value is updated and the error state is cleared if CHS is pressed).

The questions I have are

-Does the HP29C' behave in the same way..?

-Are there any other 'odd' error codes..?

-Does the HP29C return an error number as well as the error message..?

-How is the i register used to indirectly address store and (I assume) program locations..?


Mike T.


Hi Mike, My 29C just gives me "error" in the display when I attempt an operation that would overflow one of the registers. Any key clears the error message, and a review of the register reveals that the offending operation was not performed.
There are no other odd error codes that I can see.
On the 29C, register zero serves as the indirect register. Sto or Rcl (i) will access the register number (0 thru 29) stored in zero...outside that range gives an error. Register arithmatic will also work this way...Sto + (i) for instance. Registers 16 through 29 can only be accessed indirectly, and are volatile.
0 thru 9 stored in zero will go directly to the so named program label when GSB (i) is executed. If that label doesn't exist you get error in the display.
And finally rapid reverse branching...If you store a negative number (<-99) in register zero and execute GSB (i), the program counter will go backwards from it's present location that many steps and resume operation from that point. If less than -99 is in zero when you try this...you guessed it...error in the display.

One more thing...there are ISZ and DSZ functions as well, which will increment or decrement reg zero by 1, skipping the next program step if the resultant contents of register zero is 0. These two commands can be invoked programmatically or manually from the keyboard.
Best regards, Hal


My HP 19C (same as the 29C, but with a printer), gives "9.9999999 99" on overflow, (e.g. 1 EEX 55 ENTER x) and "Error" on register overflow (e.g. 1 EEX 55 STO 1 STOx 1).

There's no error number, just the message "Error".

Regarding register "i", there isn't one. Executing STO i or RCL i uses register 0 as the indirection register. (i.e. STO i on the 19C/29C is equivalent to STO IND 00 on the 41C).

Executing GTO i or GSB i does one of two things:

1) If register 0 contains 0 to 9, branches to that label.

2) If register 0 contains -1 to -99, branches backward that many steps.




My hp-29c behavies like the one of stefan (serial 1712xxxxxx)

bye, ricardo


Many thanks to those who have already responded, hopefully I will be able to put this information to good use shortly - just out of interest has anyone tried this on an HP25/25C or HP21..?

Just for completeness and in case any one is interested I generated the register overflow using the following key sequence:

STO x 0

Mike T.


The 25, 25C and 27 show "OF" on overflow during storage register arithmetic. This is documented in the manuals.

The 19C, 29C, 67 and 97 give "Error" which is also documented.

The 21 and 22 don't give any indication that you've overflowed a storage register and this is not documented in the owners manual.

Possibly Related Threads...
Thread Author Replies Views Last Post
  Usefulness of Woodstock Cs without their C Matt Agajanian 5 1,889 12-10-2013, 02:05 PM
Last Post: Geoff Quickfall
  Woodstock, Classic & Spices for iPhone Matt Agajanian 8 2,151 07-10-2013, 06:10 PM
Last Post: BShoring
  Some Observations on Geir Isene's ROM Offerings Les Wright 11 2,274 06-08-2012, 06:15 PM
Last Post: Les Wright
  A Woodstock 67 Matt Agajanian 4 1,517 05-20-2012, 10:57 PM
Last Post: Mike Morrow
  Disassemble Battery Pack 82028B (woodstock) Jacques Karensky 0 832 05-19-2012, 03:39 AM
Last Post: Jacques Karensky
  Woodstock/Spice Keyboard Cleaning Revisited Matt Agajanian 0 734 05-12-2012, 03:43 PM
Last Post: Matt Agajanian
  Woodstock parts compatiability? Russell Dobson 7 1,763 03-28-2012, 05:35 AM
Last Post: Luiz C. Vieira (Brazil)
  Cleaning keys on a Woodstock (HP-27) Geir Isene 2 1,005 10-30-2011, 03:53 PM
Last Post: Geir Isene
  HCC2011 and some 15LE observations Geoff Quickfall 4 1,196 09-23-2011, 09:21 PM
Last Post: DigiGal
  Woodstock LED question Mark Henderson 9 1,931 07-30-2011, 02:22 PM
Last Post: Mark Henderson

Forum Jump: