msp430 for low power application

I don't understand what you mean by "relation between clock frequency and power mode". AFAIK, there is no relationship: they're orthogonal.

The power management features are explained pretty clearly in the user's manuals.

Power is pretty much linear with respect to clock frequency.

What do you mean by not available? Can't you set the clock prescaler in 16 steps between /1 and /256, for example?

Do you really need to vary the master clock frequency, or can you just go into low-power sleep mode and then wake back up on either a periodic or externally generated interrupt? That's the strategy that seemed to be pretty much par for the MSP430 course, as I recall.

cellmania schrieb:

In the datasheet for MSP430F135 processor, page 25, chapter "electrical characteristics/supply current": Current consumption of active mode versus system frequency I(AM) = I(AM)[1 MHz] x f(system)[MHz] I(AM)[1 MHz] is about 300 uA. So it's pretty linear and in the ballpark for other types of mcu.

The trick of MSP430 is a fast wakeup from sleep and easy change of frequency. If you can live with the internal oscillator (DCO), you can set its frequency according to slau049.pdf, chapter "4: basic clock module" by changing DCOCTL. There are three clock lines: MCLK (clock for processor core), SMCLK (clock for peripherals) and ACLK (second clock for peripherals). Every clock line has a prescaler (DIVM,DIVS and DIVA) which divides DCO clock (/1, /2, /4 or /8). In addition to that, you can stop every clock by setting some bits in the status register. In this case the peripherals and the core are fully static and an interrupt restarts the core clock.

cheers Gunther

Just reading up on them myself. :-) The information on power consumption and modes is split between the individual datasheets and the User's Guide. I don't know which derivative you are researching, but the user's guide for the MSP430x1xxx (slua049f.pdf) has a nice picture of the clockmodule. As far as I understand it, you can only control the frequency of the DCO. But you can switch between different clock sources. There is also a description on which clocks are enabled during which power mode.

The DCO (resistance controlled oscillator) can be varied dynamically, and its basic frequency changed by switching between the internal resistance and an external one. The crystal clock can be turned off, and some variants have two crystal oscillators, so one can be a high frequency clock while the other runs from a 32kHz crystal. In addition, you can slow down (via 1/2/4/8 selectable dividers) or turn off clocks to the peripherals.

There are also 5 low power modes:

LPM0 - The CPU is disabled. LPM1 - The loop control for the fast clock (MCLK) is also disabled. LPM2 - The fast clock (MCLK) is also disabled. LPM3 - The DCO oscillator and its DC generator are also disabled. LPM4 - The crystal oscillator is also disabled.

with decreasing power, but increased wakeup time, as the number rises.

(partly from

It's all in the appnotes on the TI website, though rather distributed all over the shop.

JS

Variable frequency is allowed in AVR's and MSP430 down to very low frequecies with near linear power reduction. Other processors you can't do this (ARM Cortex for instance).

TI has a neat wireless MSP430, called the CC430 you may be interested in, see

"Has" may be a bit optimistic if you want to start development now:

"The first CC430 samples will be available in limited quantities in 1Q09 with mass-market sampling and further device introductions scheduled for later in the year"

Shame actually, since it would be an ideal fit for what we are starting now. Currently investigating msp430+cc1050 as the cc1050's internal 8051 is a bit power hungry if you want any osc running in power down.

Why cc1050 and not cc1101?

Because the cc1101 is a tranceiver and cc1050 is a transmitter, we transmit only. Receiver side will be a completely different device which will not be that power critical, so more choices for RF and CPU.

Stef,

Have you also considered the MSP430+CC2500 combination? TI offers an inexpensive development kit ($50US?) with a pair of boards, one powered from a 2xAA battery pack and the other from a USB "programming dongle".

If you're not already aware of the kit, look for TI document slau227c, "ez430-RF2500T Development Tool" for an overview and circuit diagrams.

Frank McKenney

-- I do not deny that laws are important, but...the passage of new laws has continually served as a substitute for thought. -- Aldo Leopold

-- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)

The cc2500 is 2.4GHz, we need 868MHz for our data transfer. At least that is the current selection, but things may change later. :-)

I was just searching for the required tools (compiler, devboards etc.) and found this page (well just click the 'tools' link on msp430 page ;-) ):

The kit you mention is on there as well as many others, all very affordable, even the IDE/compiler kit.