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The F5637's ADC can run off of one of several available clock signals of varying speeds. Once a sample has been captured, it is held ready in the ADC10MEMx registers for a defined number of clock cycles. Since we are concerned with a low frequency signal, we will want to slow down the ADC12 as much as possible. (Students who have had Elec241 will notice some fundamental flaws in the assumptions made regarding high-frequency noise, but in practice this has very little effect on the final results). Even in its slowest mode, the ADC12 will still sample too quickly, so the use of some kind of moving average will help stabilize its DC readings.

Controlling the adc12 in c

C basics

Your C program will be structured similarly to its assembly language counterparts, but with a much different syntax. Like before, the register names are all pre-defined in the "msp430.h" header file. To set a register, now just use an equals sign and set it like any other variable. For example, you will want to disable the watchdog timer in the first line of your program. WDTCTL=WDTPW+WDTHOLD; The compiler will execute the void main(void) function first. From that function, you can call any other functions or run any loops that you would like.

C skeleton program

#include<msp430.h>//Global Variable Declarations //Global Function Declarationsint main(void) {WDTCTL = WDTPW + WDTHOLD; // Stop WDT //Other Setup//Your Program Here //Can call other helper functions, loops, etc.return 0; }

Configuring the adc12

The ADC12 has two main control registers ADC12CTL0 and ADC12CTL1 , and 16 memory control registers ADC10MCTLx ( 12 bit ADC M emory C o N tro L 0/1/2... channel 0-15). These registers control all the timing and conversion aspects of the ADC.

Adc12ctl0

Register diagram of the ADC12CTL0 register.

In the first control register ( ADC12CTL0 ), we only need to change two parameters,

  • ADC12SHT0_x-- 12 bit ADC S ample H old T ime-- a higher value means each sample will be held for a longer period of time. We want to set this at the max value of ADC12SHT0_8 .
  • ADC12ON-- 12 bit ADC ON /OFF--setting this bit to "1" (denoted by the label ADC12ON ) turns on the ADC, a vital step to performing any conversion!
To actually do this in C, just use addition and an equals sign: ADC12CTL0 = ADC12SHT0_8 + ADC12ON ;

Adc12ctl1

Register diagram of the ADC12CTL1 register.

In the second control register ( ADC12CTL1 ), we want to set two parameters.

  • Since some of the bit labeling is inconsistent (especially between different versions of a microcontroller), it is always good to examine the header file for a controller to see how its aliases are defined before using them in your code.
ADC12CTL1 = ADC12SHP + ADC12CONSEQ_0;

Register diagram of the ADC12CTL1 register.

We also need to set the appropriate input channel to our output memory address in the ADC12MCTL0 register

  • ADC12INCH_x-- 12 bit ADC In put Ch annel # -- this 4 bit section determines which of the possible input channels the ADC will actually convert and store into the ADC12MEM0 register.
ADC12MCTL|= ADC12INCH_0;

Lastly, analog conversion must be enabled on the input ports themselves. These act as gates to prevent leakage current from flowing from a pin set as an output through the ADC to ground-- a substantial waste of power. To enable the ADC for your desired GPIO pin, just set the corresponding bit in P6SEL ( P ort 6 Special Function SEL ect) to "1". P6SEL |= BIT#;

For more info about the ADC12's configuration options, see the MSP430 manual starting on page 742.

Using the adc

To read a sample from the ADC, just read from the ADC12MEM register after the sample has completed. while (ADC12CTL1&ADC12BUSY); // Wait in naive loop for conversion to complete my_var= ADC12MEM0; Remember that we have setup the ADC for single conversion and hold, so if you want another value, you will have to tell it to sample and convert again. You do so by modifying two values in ADC12CTL0:

  • ADC12ENC-- 12 bit ADC En able C onversion-- locks in the ADC settings and stabilizes it for conversion.
  • ADC12SC-- 12 bit ADC S tart C onversion-- setting this bit to one actually triggers the ADC's conversion cycle.
ADC12CTL0 |= ADC12ENC + ADC12SC;
Be sure to use OR equal (|=) so that the configuration bits you set before don't get overridden.
Also, don't forget to configure P3 as usual. You will need to set the pins you wish to use as outputs in the P3DIR register to display a value on the LEDs. You can configure the P3 registers using aliases and variable assignments just like with the ADC registers.

Assignment details

Using Code Composer Studio 5, write a C language program turning your MSP430 ESCAPE Platform into a simple 10 level voltmeter. Your program should divide the 0-3.3V input range of the ADC into 10 zones, and then output from a 0 to a 9 on the LED display depending on the input voltage from the light sensor. Don't worry about a value landing on the boundary between two zones, just deal with it consistently. Test your volt meter by sampling pin P6.0 and exposing it to different light intensities.

Your Program should consist of:

  • A "void main(void)" function that drives your program
  • A successful setup routine that properly configures the ADC12
  • An output routine that loop infinitely and successfully re-scales the 4096 ADC possibilities to 10 zones

Questions & Answers

what is the coefficient of -4×
Mehri Reply
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
Akash
College algebra is really hard?
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Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
Carole
I'm 13 and I understand it great
AJ
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Atone
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Adu
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
Vedant
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
Augustine
how do they get the third part x = (32)5/4
kinnecy Reply
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
AJ
how
Sheref
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
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But this is not salma it's Faiza live in lousvile Ky I garbage this so I am going collage with JCTC that the of the collage thank you my friends
salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
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salma
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Hello
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Ali
greetings from Iran
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salut. from Algeria
Bach
hi
Nharnhar
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
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Abdirahman Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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Source:  OpenStax, Elec 220 lab course (escape). OpenStax CNX. Apr 07, 2013 Download for free at http://cnx.org/content/col11513/1.1
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