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Explains how the digital-to-analog converter works on the MSP430.

The MSP430F169 is equipped with two digital to analog converters (DACs) on general I/O port 6. A DAC converts an unsigned integer into an analog voltage within the capacity of the MSP. As in all cases with the MSP, the complete details are found in the MSP430 Family User’s Guide from the Texas Instruments website www.ti.com .

Voltage range and precision

Unlike the ADC on the MSP, the DACs have variable bit precision of either 8 or 12 bits. The range is also controllable as either one or three times the voltage reference. The voltage reference is also selectable. All bits for controlling voltage reference, scaling, and precision can be found in the DAC12 Control Register (DAC12_xCTL). In most cases, 12 bit precision is desirable.

In the MSP430 architecture there are two general sources for a voltage reference: VeRef and Vref. VeRef is an externally supplied voltage, but Vref is generated by the MSP itself. Because the 226 board does not provide the MSP with a VeRef voltage, the only voltage reference available for the DAC and ADC is the Vref. This restricts the choices for the SREF bits of the DAC control register to the Vref choice. Additionally, the Vref voltage reference for the DAC comes from the ADC module. This means that it is necessary to turn on the voltage reference in the ADC control register (ADC12CTL0) with the REFON bit.

Operating modes

The DAC competes with two of the ADC channels for access to the pins of I/O Port 6. Unlike most peripheral controls on the MSP430, the DAC’s access to the pins is not controlled by the PxSEL register. Instead, the DAC is multiplexed with the ordinary port control and will drive the output if the DAC12AMPx bits are set to any value greater than zero. The DAC12AMPx bits in the control registers also determine the mode of the DAC’s operation.

  • Mode 000 The input buffer is off. The DAC is off, and the output buffer is high impedence.
  • Mode 001 The input buffer is off. The DAC is off, and the output buffer is 0V.
  • Modes 010 - 111 Each step in mode increases the power consumption of the DAC while improving the settling time of the module.
The two most useful modes for these labs are modes 000 and 111. Because our devices are not battery powered, we can afford the power consumption to improve speed. Mode 000 is needed to turn off the module when necessary.

Using the dac

The basic method of DAC operation is to load the DAC12_xDAT. Using the DAC12LSELx bits of the control register, the actual trigger for the output is set. The device can be figured to output whenever the data register is written to, whenever the data register is written and the DAC enable is set, or according to timers A or B. It is necessary to change the mode out of SEL mode 0 in order to use the interrupts with the DAC.

The DAC can be interrupt enabled via the DAC control register and the interrupt enable registers. The flag is set whenever a conversion is complete. Also, the DAC outputs can be grouped together to ensure that the output of both DACs appears simultaneously. When the units are grouped, both DAC12_xDAT registers must be written before the outputs will appear. The device does not check whether you have changed the value; updating with the same information will still work.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
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biomolecules are e building blocks of every organics and inorganic materials.
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research.net
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sciencedirect big data base
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Introduction about quantum dots in nanotechnology
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nano basically means 10^(-9). nanometer is a unit to measure length.
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Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
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s.
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for screen printed electrodes ?
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s. Reply
of graphene you mean?
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or in general
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in general
s.
Graphene has a hexagonal structure
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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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