|Re: HP 20b Business Consultant calculator announced|
Message #10 Posted by cyrille de Brébisson on 11 June 2008, 9:16 a.m.,
in response to message #2 by DaveJ
le me try to answer a bunch of things at once, to make it easier...
- agregated questions about CPU speed and battery issues:
Yes, it is running at 30Mhz while doing calculations. With few exceptions, calculations are done in less than 100ms (even IRR type stuff, the longest calculations are, surprisingly enough, probability distribution ones)... the battery drain is large at these frequency (15mA or so), and that is why we are using 2 battery. since 1 CR2032 is rated for a pulse current of 20mA for 15s, this is in theory completely OK...
As soon as calculations are finished, it pretty much shuts down (ie, all gets powered off with the exception of the screen).
- question about 15Mhz flash speed:
Flash speed is 15mhz and CPU is 30Mhz, BUT most of the code is in thumb mode where instructions are only 16 bits, so thumb code does execute at the full 30Mhz. some of the critical loop code is in ARM mode, but that is also OK thanks to the buffer and small cache that allows that code to also run at full speed even at 30Mhz.
- My only complaint would be the battery life. 9 months doesn't cut the mustard IMHO. They should have used AAA's.
the calculator is the thickness of a AAA! using AAA would have made the unit significanly bulkier and not as 'pretty'...
- losses in the internal battery resistance, (in the order of 20-40ohms):
datasheets indicate <10ohms (typically 7ohms)... you of course need to divide this by 2 since there are 2 battery in parallel, so typically 3.5 Ohms...
as a result, although, there is still a *10 of the power consumption in the battery at higher speed, that consumption is negligeable compared with the CPU consumption.
- Going by the low-res pictures, it looks like they used a 7-segment numerical display. If so, I applaud them: it should be much more readable than dot matrix.
there is both a large dot matrix (ie: large dox, small matrix) on the top line and a 7 segment display at the bottom for full 12+3 accuracy display (12 digits, 3 exponents).
- Again I am not amused about HP's price policy for Europe.
it's not the HP price policy. remember, HP is not allowed to 'fix' prices, that would be illegal (and conveniently called... 'price fixing':-). also remember that you will pay an extra 20% or so in europe due to VAT while the US price are always given with no tax...
- Has anyone noticed the AT91SAM7L128 micro used has 128KB of internal FLASH program memory (well, yes, I have!)
There might be the potential here to reprogram the unit to customise it, as was recently discussed about the 35S.
yes, there is a potential, and conveniently enough, the poor engineers have inadvertently left the footprint for the JTAG port on the final PCB, so you can easely open the calculator, connect a JTAG and go hacking happily! But I guess we will find someone in the group to complain about the 'lack of finish' and HP shipping stuff that is 'barely more than prototypes' because of that!
- Anyone opened one?
nope, I have opened 100's... but that is just me bragging :-)