HP 12C ATSAM4L version: ON-f-ENTER

[brouhaha]

I was trying to remember the key sequence to get the firmware version of ARM-based HP 12C calculators (which starts with ON-g-ENTER), and before I hit upon the right combination, I tried ON-f-ENTER. After doing that, the 12C behaved normally, except that it would not turn off. The ON key after that was completely ignored, until I reset the calculator.

Has anyone else noticed this? I've only tried this on a recent ATSAM4LC2C based 12C, not the earlier ATSAM7L128 version. It seems to be reproducible. I imagine it's intended as some kind of factory or R&D test mode.

Some might find it amusing that I discovered this by accident when poking keys with my fingers, and not by spelunking through the firmware.

[Mark H. Shin]

(03-06-2023 08:07 AM)brouhaha Wrote:  Has anyone else noticed this?

Confirmed.

For both Philippines (S/N PHA...; ChE -- d1d1h; 2015-01-30) and China (S/N C1G...; ChE -- 0F0Fh; 2015-01-08) production, calculator cannot be turned off without reset.

[rprosperi]

This was found and reported by (of course) Joe Horn last year. Note that it also disables the auto-power-off feature after some number of minutes. To re-enable the ON key, press and hold f+ENTER then press ON.

There's no info if this was done on purpose (e.g. for diags or battery life testing, etc.) or if it was a simple bug. The fact that the mode can be both enabled and disabled suggests it was there for some purpose, but there were other deleterious side-effects noted (some functions performed more slowly) so probably best to NOT use this "feature".

[Mark H. Shin]

(03-06-2023 03:38 PM)rprosperi Wrote:  probably best to NOT use this "feature".

Another thing I noticed, running the iteration test program, while operating in this "feature" mode, the "running" displays continuously...

[brouhaha]

(03-06-2023 03:38 PM)rprosperi Wrote:  This was found and reported by (of course) Joe Horn last year.

I'm not at all surprised.

Quote:Note that it also disables the auto-power-off feature after some number of minutes.

I suspected that it might. I didn't leave it on to find out, because I thought it might also have increased power consumption compared to normal mode, though I haven't tried to determine whether that is the case.

Quote:To re-enable the ON key, press and hold f+ENTER then press ON.

That seems to behave in an inconsistent manner on my unit. I've seen:

1) does nothing, calculator still in forced-on mode
2) calculator turns off, and at the next power-on, gets "Pr Error" (memory lost)
3) calculator turns off, then calculator won't turn on for a while, or perhaps some number of repeated attempts
4) calculator turns off, then ON key turns it on normally

I assume that #4 is the intended behavior, but in my experience that's the least common outcome.

Quote:There's no info if this was done on purpose (e.g. for diags or battery life testing, etc.) or if it was a simple bug.

It seems highly unlike that it's a just a bug.

Quote:The fact that the mode can be both enabled and disabled suggests it was there for some purpose, but there were other deleterious side-effects noted (some functions performed more slowly)

Interesting! I didn't poke at it enough to discover that.

Quote:so probably best to NOT use this "feature".

Agreed. It's clearly not intended for users.