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We will explore a energy-efficient way of measuring time by using timers. A timer is a register which counts up to a certainnumber at each clock tick. During this, the MSP430 can switch to a low-power mode. Each time the timer threshold isreached, a timer interrupt wakes the MSP430, which toggles the two LEDs.

Running the code

  • Copy the code presented below Alternatively, this code is available in the downloadable source code . Open source_code/iar_v4.11/lab_ezwsn.eww with IAR. The project corresponding to this section is called led_timer . .
  • Compile and download the code onto the board (Ctrl+D) .
  • Let the code execute (F5) , both LEDs should blink.

#include "io430.h" #include "in430.h"int main( void ) {WDTCTL = WDTPW + WDTHOLD; P1DIR |= 0x03;BCSCTL3 |= LFXT1S_2; TACCTL0 = CCIE;TACCR0 = 1000; TACTL = MC_1+TASSEL_1;__bis_SR_register(GIE+LPM3_bits); }#pragma vector=TIMERA0_VECTOR __interrupt void Timer_A (void){ P1OUT ^= 0x03;}
Blink LEDs using timer interrupts

Some keys for understanding the code:

  • Line 7 switches on the ACLK by sourcing it to the VLO , a very low power crystal oscillator inside the MSP430, different from the more accurate and energy hungry DCO (Digitally Controlled Oscillator). The DCO drives the MCLK and the VLO the ACLK. ACLK is used for the timer; MCLK for executing code.When there is no code to be executed (i.e. when waiting for interrupts), a low power mode (in which DCO is switched off) can be used.
  • Line 8 enables interrupts for Timer_A .
  • Line 9 sets the value up to which Timer_A will count.
  • Line 10 tells Timer_A to count up ( MC_1 ) each time ACLK ticks ( TASSEL_1 ).
  • Line 11 enables interrupts globally and enters LPM3. Note that LPM3 leave only ACLK running, which is exactly what we need because our Time_A runs off ACLK.

Measuring time

We use extension pin P6 to measure time exactly. Therefore:

  • add line P2DIR |= 0x08; after line 6 to declare P2.3 as output;
  • add line P2OUT ^= 0x08; after line 16 to toggle P2.3 after toggling the LEDs;
  • connect a probe of your oscilloscope to extension port P6 , ground on extension port P1 . Power on the board, you're now able to read the duration between two toggles.
  • reprogram your board with TACCR0 values between 1000 and 30000; verify that the times obtained are close to the following:

Duration when using timers
TACCR0 value measured toggle duration
500 47.40ms
1000 95.00ms
10000 950.0ms
20000 1890ms

This table informs you that 1000 ACLK cycles take 95.00ms, one ACLK cycle thus takes 95μs, the VLO on the MSP430 thus runs at 10.5kHz. In theory, the VLO runs at 12kHz; the exact value depends on the voltage of the batteriesand on the temperature.

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
I'm not good at math so would you help me
what is the problem that i will help you to self with?
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Ezwsn: experimenting with wireless sensor networks using the ez430-rf2500. OpenStax CNX. Apr 26, 2009 Download for free at http://cnx.org/content/col10684/1.10
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