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Describes how the clock system works on the MSP430.

The clock system on the MSP430 is designed to be flexible and low power. The implementation of these goals is largely based on the ability to select different clocks for different parts of the chip. By choosing the minimum clock speed necessary for a given module, power consumption is reduced and the particular synchronization needs of the module can be met.

The MSP has three clock sources for the clocking system, and three clock lines that chip systems can choose between. The clock sources are used as the basis for the clock lines, and this allows for a mix of slow and fast clocks to be used around the system. The three clock sources are:

  • Low Frequency Crystal Clock (LFXTCLK) – this signal is meant to come from a watch crystal external to the MSP itself. The crystal connects to the XIN and XOUT pins, and the intended oscillation is 32kHz. This is the source of the Auxiliary Clock line (ACLK). The primary control of this source is that it can be turned off with the OSCOFF option in the Status Register. The source also has a high-speed mode for faster crystals.
  • Crystal 2 Clock (XT2CLK) – this signal is the second external clock source, and it is connected to the XT2IN and XT2OUT pins. In our case, the source is connected to a 7.3MHz crystal. In general, this signal is meant to be the high-speed clock source. This source can be turned off with the XT2OFF bit of the Basic Clock system control register 1 (BCSCTL1).
  • Digitally Controlled Oscillator Clock (DCOCLK) – this is the only internally generated clock input, and it is the default clock source for the master clock upon reset. By default this clock runs at about 900kHZ, but the RSELx, MODx, and DCOx bits allow this to be divided down or even blended to achieve a lower clock frequency on average.

The three clock lines are:

  • Master Clock (MCLK) – This clock is the source for the MSP CPU core; this clock must be working properly for the processor to execute instructions. This clock has the most selection for its source. The source is selected with the SELMx bits of the Basic Clock System Control Register 2 (BCSCTL2). The divider is controlled with the DIVMx of the BCSCTL2. Finally, the CPU can be turned off with the CPUOFF bit of the Status Register (SR), but to recover from this state an interrupt must occur.
  • Submaster Clock (SMCLK) - This clock is the source for most peripherals, and its source can either be the DCO or Crystal 2. The source clock is controlled with the SELS and SCG bits of the BCSCTL2 and SR. The divider is controlled by the DIVSx bits of the BCSCTL2.
  • Auxiliary Clock (ACLK) - this clock line’s source is always LFXTCLK. It is an option for slower subsystems to use in order to conserve power. This clock can be divided as controlled by the DIVAx bits of the Basic Clock System Control Register 1 (BCSCTL1).

The MSP clock system has dividers at the beginning of its clocks, and at most peripheral destinations. This allows for each module to keep a separate timing scheme from other modules. This is often necessary for off chip buses because these systems have to meet a variety of speed requirements from the outside. For educational purposes the fastest clocks are usually the most useful, but power consumption is the primary cost of high speed clocks.

Clock dividers

Throughout the MSP clocking system there are clock dividers. A clock divider reduces the frequency of an input clock and outputs this divided frequency. The simplest dividers work on multiples of two, so the output might be a square wave of half, one quarter, or one eighth the input square wave’s frequency.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Microcontroller and embedded systems laboratory. OpenStax CNX. Feb 11, 2006 Download for free at http://cnx.org/content/col10215/1.29
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