Re: 2 articles about it


Hi all,

after browsing some of the wonderful PPC CDs within the last nights I found an appropriate article in Datafile Vol.5, No.2, March, April 1986.

It's from Mark Power and says:

"Screen Scroll Bug
I have recently discovered a bug in the error handling of my HP41CV (serial number 2349S40141). The problem is demonstrated by running the program given below.


02: CLX

03: "** HP41-CV *"


05: LBL 01

06: SF 25 (Ignore error)

07: SIN (Short delay)

08: GTO 01 (No LBL error)

09: GTO 01 (Do it again)

10: END

It seems that the calculator forgets that there is a message on the screen and treats it like the running symbol and scrolls the screen when the machine performs the GTO which creates he error.
If you stop the program and look at the ALPHA registers you will see that the original message is still intact. This bug is not of great importance but I hope someone will put it to good use.

Mark Power"

There follows a remark from the editor:
"(Ed - This is one of the display bugs which all HP41's have. These bugs are described in Appendix C of "Extend Your HP41".)"

Now let's take a look into W.A.C. Mier-Jedrzejowicz' great book:

"Display bugs

If you VIEW or AVIEW something and execute an instruction that clears flag 25 then the contents of the display will move around just as if they were the "flying goose". Enter and run the following short program:

LBL "DSPL", PI, SF 25, "?", AVIEW, SF 60, LBL 01, ATAN, GTO 01, END

SF 60 generates an error and clears flag 25. Flag 50, the message flag is cleared at the same time, but the display is not cleared, so the HP-41 acts as if the display had been cleared and the "flying goose" was in it, but actually moves whatever is in the display. The ATAN is just a delaying tactic, without it the display would move too quickly in the LBL 01 loop. You can use this bug to display your favourite message while a program is running, but the message must not be more than 12 display positions long (it can contain extra punctuation though). You can experiment with interesting displays, for example try the string " . , . , . , . , . , . ," instead of the "?" in the program above. Reference: PPCCJ V6N8P24"

That's for the moment. Now we have 3 different examples for creating this nice effect and there is no more need to wonder about flag 99 ;-)
In case I find more interesting articles about this fyling goose replacement I'll let you know.

Best regards and happy programming


Edited: 23 July 2003, 4:28 a.m.

Possibly Related Threads...
Thread Author Replies Views Last Post
  Couple of new HP-17bii solver programs in Articles Don Shepherd 27 2,400 01-22-2012, 11:09 PM
Last Post: Don Shepherd
  Updated: Some press articles about the new 30th anniversary 12c Gene Wright 13 1,176 09-01-2011, 08:57 PM
Last Post: gene wright
  HP Solve Issue 19 available - has several articles by museum forum contributors! Gene Wright 17 1,508 07-03-2010, 09:16 PM
Last Post: Diego Diaz
  Loop of + benchmark now in Articles section Gene Wright 10 1,001 06-08-2010, 05:40 AM
Last Post: Frido Bohn
  Interesting (Floating Point) Math Articles Giancarlo (Italy) 7 703 12-14-2007, 01:30 PM
Last Post: Rodger Rosenbaum
  HP-35 and CORDIC-articles at Dr. Dobb's Karl-Ludwig Butte 2 399 11-25-2007, 04:11 AM
Last Post: Karl Schneider
  Two new articles in next Datafile issue Valentin Albillo 8 692 10-12-2007, 04:48 PM
Last Post: Dave Colver
  Back from vacation and 4 new articles online ! :-) Valentin Albillo 28 2,321 08-23-2007, 09:06 AM
Last Post: Valentin Albillo
  Two new Datafile articles online (PDF format) Valentin Albillo 6 604 04-27-2007, 01:48 PM
Last Post: Tony Duell
  Two additional articles online: Minimax & Sudoku Valentin Albillo 4 527 07-27-2006, 04:03 AM
Last Post: Valentin Albillo

Forum Jump: