HP-42S Fast Mode under program control

Update 2/2012 - WARNING: I received an email indicating that the procedure listed further down rendered an HP-42S inoperational for good! So it may in fact not be a good idea to try it. 

You have been warned, do this only on your own risk!!

Update 6/12/97!!!! I was unaware, but apparently, HP made some changes in the ROMs of the HP-42S that make it such that the PROGRAM listed below will NOT work on all HP-42S. It will stop with an error message. The technique CAN still be done manually as described in the article, but only do steps 1-7 of the "First Time Set-up". Sorry for the trouble!
The HP-42S contains a location accessible using the built-in debugger that controls processing speed. This value can be changed to speed up (or slow down) the machine with no damage to the HP-42S that anyone has ever reported, except less battery life when running at the fast speed. All programs run much faster and the equation solver is a joy to watch!

Note: If you do this incorrectly, you can make the calculator lose it's memory with a "Memory Lost" message. I'm not responsible for any problems!

First Time Setup

  1. Set the machine to your desired contrast by using the EXIT and + or - Keys.
  2. Perform a CLV "REGS", then press E+ (Sigma Plus).
  3. Enter the Debugger by pressing EXIT and LOG at the same time and press the back arrow key. (WARNING: Do NOT press any keys other than those listed next. Doing so might alter program memory and result in a MEMORY LOST!). If you are careful, this will not happen.
  4. Using the /, *, +, and - Keys, move to address 40300. (The address is shown on the left side of the display).
  5. When this is showing, press the "F" key (The top right key).
  6. Return to address 00000 by using the /, *, + and - keys.
  7. When the display shows the 00000 address, exit the debugger by pressing the decimal point "." key.
  8. Key in 16248, RCL IND X, STO "FAST".
  9. Key 8124, RCL "FAST", STO IND Y. (Note: Display will say "Machine Reset". This is not a memory lost condition.)
  10. Test by pressing BEEP. Notice how fast the BEEP sounds? You’re running at 2X speed.
Program to automatically put the machine into Fast Mode

Once you've done the initial setup, you can key in this program. Running this program will automatically put you into Fast Mode.

LBL "Fast", SIGN, SF 25, CLX, RCL "REGS", SIZE 0000, SF 25, Sigma+, 8124, X<>"FAST", STO IND "FAST", X<>"FAST", RDN, SF 25, STO "REGS", RDN, LAST X, END.

That's it. The instruction RDN is Roll Down. Otherwise, this is easy.

What takes you out of fast mode? If you press the EXIT key for ANY reason, you’re put back into normal speed mode. For most menu purposes, you can get out of them some other way, or you can always rerun the program above to get faster.