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The G2231's ADC can run off of one of several available clock signals of varying speeds. The ADC10 also has a clock divider that can further slow the conversion speed by up to a factor of 8. Once a sample has been captured, it is held ready in the ADC10MEM register for a defined number of clock cycles. Since we are concerned with a low frequency signal, we will want to slow down the ADC10 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 ADC10 will still sample too quickly, so the use of some kind of moving average will help stabilize its DC readings.
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
"msp430x20x2.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.
#include "msp430x20x2.h"
//Global Variable Declarations//Global Function Declarations
void main(void){
WDTCTL = WDTPW + WDTHOLD; // Stop WDT//Other Setup
//Your Program Here//Can call other helper functions, loops, etc.
}
The ADC10 has two main control registers
ADC10CTL0 and
ADC10CTL1 , and two analog input enable registers
ADC10AE0 and
ADC10AE1 (
10 bit
ADC
A nalog
E nable
0/1 ). These registers control all the timing and conversion aspects of the ADC.
In the first control register (
ADC10CTL0 ), we only need to change two parameters,
ADC10SHT_3 .ADC10ON ) turns on the ADC, a vital step to performing any conversion!ADC10CTL0 = ADC10SHT_3 + ADC10ON ;
In the second control register (
ADC10CTL1 ), we want to again set two parameters, but we will need to use 4 alias labels instead of just two.
ADC10CTL1 = ADC10DIV0 + ADC10DIV1 + ADC10DIV2 + INCH_X;
Lastly, the ADC10 has the ADC10AE0/1 registers that enable analog input on the different pins. 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
ADC10AE0 to "1".
ADC10AE0 |= BIT#;
For more info about the ADC10's configuration options, see the MSP430 manual starting on page 609.
To read a sample from the ADC, just read from the ADC10MEM register after the sample has completed.
my_var= ADC10MEM; 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 ADC10CTL0:
ADC10CTL0 |= ENC + ADC10SC;
P1DIR register as well as the
ADC10AE0 register. You can configure the P1 registers using aliases and variable assignments just like with the ADC registers.Using Code Composer Studio 4, write a C language program turning your MSP430 LaunchPad 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. Don't worry about a value landing on the boundary between two zones, just deal with it consistently. Test your volt meter by attaching it to some of the variable power supplies around the room. DO NOT EXCEED AN INPUT VOLTAGE OF 3.3V . You will damage your circuits and destroy your MSP430.
Your Program should consist of:
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