HP42S freeze after "Fast mode"


I have an HP42S bought just after it was introduced, ROM version A1.

I attempted to enter the "Fast" mode which resulted in the HP42S freezing up (not responding to any keypress of any kind) and leaving the unit without batteries for a day or so was necessary to recover completely. I am curious to see if any wizards out there can help me figure out what happened.

When running through the memory in the debugger, I used the "up" and "down" buttons (to skip by 0x1000) in addition to the four buttons mentioned in the recipe.

When out of the debugger, I fumbled around a bit before finding the "IND" for "RCL IND X" (my HP is a bit rusty)

After step 9 ("STO IND Y"), the calculator blanked completely and did not respond to any keypresses

Leaving the batteries out for a couple of minutes did not change anything. Leaving them out for an hour or so returned the calculator to usability, but with some curious lingering effects.

The printer symbol was lit when turning on. It did not extinguish from regular use.

Attempting any function from the PRINT menu displays "Printing Is Disabled" and clears the printer symbol from the screen.

Whenever entering PRGM mode, the printer symbols lights up again, and again will only extinguish when attempting a print operation.

When running a program, the IR symbol (((.))) also lights up.

Leaving the unit without batteries for several hours appears to have restored the unit to normal and no obvious harm has been done to it. Still, I am curious what I did to make it react so, and what else I could have done to recover.




Bear in mind that there's a reason why HP didn't set the standard speed to the maximum, which is that they couldn't guarantee that they would work. "Fast mode" works by setting a register to an unsupported value.


IIRC, the ((.)) symbol is not an IR (infrared) indicator. The printer is the only official IR application, and it has its own annunciator. The ((.)) annunciator always flashes as a "running program" indicator.


Right you are. It has been years since I played with this device, and I don't even know where the IR printer is anymore...

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