Not remotely an HP calculator, but...

[jebem]

For completeness here are some current consumption measurements.
I was curious to find out how current efficient is this SoC processor.

Setup:
Digital current meter set to read DC Average and Maximum values, inserted in series with a external 3VDC power supply.
Now, I know this is not the correct tool to get a more precise view of the current consumption, as the machine load has a strong RF pulsating current component that would require an oscilloscope or equivalent equipment for this job. But I believe the chosen method is enough to have a rough idea of the average current consumption.

In power off state:
Maximum/Average = 0µA (well, less than 0.1µA which is the current meter resolution)
This will maintain the register memories contents while it is in off sate.

Note: While taking measurements, I noticed that the SoC is not loosing the replay buffer and the display contents if removing the power supply for a minute or so.
In fact I had to use the Reset button to recover from apparent system hang a couple of times. IMHO, this indicates a very high quality, low leakage, semiconductor substrate.
If only the designers had installed a external capacitor to filter/stabilize the battery power supply! This would also allow to change the AA batteries without losing any memory contents.


Power ON:
Maximum = 399µA (During power on)
Average = 16.8µA (at idle, no keys pressing)

Typing keys:
Maximum = 80µA

Doing miscellaneous calculations:
(arithmetic, trigonometric and factorial calculations at a rate of 3 seconds per operation, during 3 minutes)
Maximum = 120µA
Average = 84µA


AC current readings:
Setting the current meter to AC readings, the values observed were around two times higher, which I would say it is normal (but my current reader is bandwidth limited to 100KHz, so it is not really capturing the faster current peaks in the RF region where I believe the processor runs - I had no time to use my oscilloscope to take further readings).


So I would say this is a very efficient SoC design, at least from the point of view of current consumption. The AA battery cells should last for years if they don't leak before that.