HP calcs with clock

[Marcus von Cube]

(07-16-2014 09:56 AM)x34 Wrote:  

(07-16-2014 08:32 AM)walter b Wrote:  And the HP-20b and -30b also feature a RTC which allows the WP 34S to provide a stopwatch etc. Please see there.

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Sure, 20b/30b are in the list.

To add some more info here:

The Atmel chip in the 20b/30b has a built in RTC but the stock firmware for the business calculators just don't use it because it needs the crystal oscillator to be reliable. (The same is true for all HP models using the same chip such as the recent 12C, 15C LE, 10bII+.) The RTC keeps the time as long as the processor is at least in one of the low power modes and not completly turned off.

The 34S stop watch is not based on the RTC circuit. It is just a piece of software that uses the periodic interrupt. It's only useful (and enabled) on a modified calculator as is the RTC.