Environmental Engineering Reference
In-Depth Information
Use of Sleep Modes
and high resolution clock is very high. If such
accuracy is not needed for a particular task the
accurate clock is replaced by an inaccurate, low
resolution and low power clock.
MSP430 Microcontroller optimizes its efficiency
by sleeping in-between its active states. To under-
stand how efficiency can be increased by sleeping
we take an analogy. Suppose a group of students
utilize the class hours very efficiently. They go
for catnap, slumber or a deep sleep depending on
the situations. Instead of waiting for the teacher's
turn-up they go for a catnap. As soon as the teacher
appears they get up and give a warm welcome to
the teacher. When the roll-call goes on they go
for deep sleeps. A student wakes up and responds
only when her roll number is called. As teaching
starts they wake up and fully concentrate. When
a problem is given to these students they solve
it fast. While the remaining students solve the
problem they go for a slumber. All the teachers
who encourage unconventional but fruitful ideas
shall definitely accept this one.
Like these students an MSP430 microcontroller
goes for a sleep when there is no activity. There
are some applications where long inactive period
prevails. There can be a burst of activities for a
short period. Consider a robot in a factory whose
task is to detect and control fire. Fire does not
break everyday. The robot happily sleeps. When
it detects smoke due to fire it wakes up instan-
taneously. It senses the temperature and uses the
appropriate fire extinguisher. After extinguishing
the fire again it goes for a sleep. MSP430 is ideal
for this type of applications. For it, sleep means
some of the parts of the chip become temporarily
inactive and consume no power. It has several
sleep modes. Depending on the task at hand it may
go for a burst of activities. After task completion
it selects one of the most suitable sleep modes.
Single Chip Solution
Other than the standard blocks of a Microcontroller
shown in figure 1, MSP430 has additional blocks
giving additional capabilities. It can sense analog
voltages. A conventional microcontroller can
sense only digital signals in the form of 1011---.
Sensor outputs are normally analog in nature. To
interface the sensor to the I/O there should be
one Analog to Digital Converter or ADC chip in
between. Instead of using an additional ADC chip
the block is provided in the MSP430 chip itself.
These eliminate the power dissipation in the wires
or metal lines on a PCB connecting the two chips.
It also provides Digital to Analog Converter or
DAC, operational amplifiers different sensors
on a single chip (Baker, 2002; Bell, 2007; Gray,
2001; Sze, 1981).
NEED FOR UNDERSTANDING
The efficiency of MSP430 is fully manifested
when the attractive features are fully utilized. For
this reason a user or a programmer should under-
stand how MSP430 works as a low power yet high
speed microcontroller. Suppose a programmer is
developing a code for the fire fighting robot. The
program flow of figure 2 (a) is an inefficient one.
Here the microcontroller waits for the smoke.
The wait is likely to be a long patient wait. As
it remains fully active, power consumption is
almost as high as an ordinary microcontroller. In
the power saving program flow shown in figure
2 (b) the microcontroller sleeps when there is no
task. This is likely to be a long deep sleep and
enormous amount of power gets saved.
Use of Suitable Clocks
The task of a microcontroller is synchronized to
the tick of a clock. MSP430 uses different types
of clocks. The power consumption of an accurate
