Connexions module: m12145 1

Introduction to Programming the

MSP430
∗

adrian valenzuela
This work is produced by The Connexions Project and licensed under the
†
Creative Commons Attribution License

Abstract
This is a basic tutorial on how to program the basic digital peripherals on the MSP430 on the

MSP430F16x Lite Development Board.

1 Conguring Digital I/O

Digital I/O such as the LEDs and pushbuttons are congured by modifying a several registers pertaining to
the port that they are attached to. Check the datasheet to nd the respective port number of the peripheral
you which to control. For more detailed information about Digital I/O on the MSP430 check Chapter 9:
Digital I/O of the User's Guide . 1

First, we must assign the direction of the corresponding I/O pins. This is done by setting the direction
register, PxDIR, with the appropriate bit. By default, all I/O pins are assigned to be inputs.
• Bit = 0: The port pin is switched to input direction.
• Bit = 1: The port pin is switched to output direction.
On the MSP430F16x Lite Development Board the three LEDs are located on Ports 1 and 2. The port
2

number will correspond the to x value in registers such as PxIN, PxOUT, or PxDIR. Therefore, if we
wanted to dene the direction of a pin on port 2 we would write to P2DIR.
Exercise 1 (Solution on p. 3.)
How do we switch the three pins (P1.7, P2.2, and P2.3) corresponding to the LEDs to be outputs?
Output pins may be toggled using the PxOUT register. LEDs are turned on by setting their corresponding
register bits low.
Exercise 2 (Solution on p. 3.)
How would be turn on the three LEDs without modifying any other bits in the register?
Since all I/O registers are set as inputs by default we do not have to set the direction of the push buttons.
Each time an input is toggled a bit in PxIN will be modied.
Exercise 3 (Solution on p. 3.)
Write a couple dierent polling schemes for detecting if BUTTON_1 was pushed.
∗ Version 1.4: Jul 7, 2007 10:33 pm GMT-5
† http://creativecommons.org/licenses/by/1.0
1 http://focus.ti.com/lit/ug/slau049e/slau049e.pdf
2 "The MSP430F16x Lite Development Board" <http://cnx.org/content/m12796/latest/>

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note: PxIN bits corresponding to the push buttons are high by default (i.e. the button is not
depressed.)
Exercise 4 (Solution on p. 3.)
Now we will write a program that lights up one of the LEDs and will light up a dierent LED once
BUTTON_2 is pressed. The LED sequence should go as follows: red, green, yellow, repeat.
Create a new project in CrossStudio and make sure you select the correct processor, the
MSP430F169.
Include the correct header le by adding the following line at the top of the main.c le.
#include <msp430x16x.h>
It may be helpful to dene some macros for commonly used register values. For example, if we
add #define red_on ∼0x04 to the top of the le (after the #include) we may call red_on every
time we wanted the value ∼0x04. Similarly, you may write a function to turn a light on or o.
Complete the program.

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Solutions to Exercises in this Module

Solution to Exercise 1 (p. 1)

P1DIR |= 0x80;
P2DIR |= 0x0C;

0x0C in hex is equivalent to 0b00001100 in binary. Similarly, 0x80 = 0b10000000. You may refer to the
module about Binary and Hexadecimal Notation to learn how to do this conversion or you could use the
3

Windows Calculator (Start -> Run... -> Calc) to do it much more quickly. We can now easily see that
P1.7, P2.2, and P2.3 are set to 1 which makes them outputs.
note: It is helpful to use |= instead of = because it won't overwrite bits that are not set to 1 in
the mask.
Solution to Exercise 2 (p. 1)

P1DIR &= ∼0x80;

P2DIR &= ∼0x0C;

This will turn on all three LEDs assuming they had already been set to be outputs.
note: ∼0x0C = 0xF3 = 0b11110011
Solution to Exercise 3 (p. 1)
while(!(P2IN&0x01)); or if (!(P2IN&0x01));
Solution to Exercise 4 (p. 2)

#include <msp430x16x.h>

void main(void)
{
P1DIR |= 0x80; // Set P1.7 as an output pin
P2DIR |= 0x0C; // Set P2.2 & P2.3 as output pins

P1OUT |= 0x80;
P2OUT |= 0x0C; // Turn off all LEDs

while(1){
P1OUT |= 0x80; // turn off yellow LED
P2OUT &= ∼0x04; // turn on red LED

while(P2IN&0x02); // waits here while button isn't depressed

while(!(P2IN&0x02)); // waits here while button is pushed in

P2OUT |= 0x04; // turn off red LED

3 "The MSP430F16x Lite Development Board" <http://cnx.org/content/m12796/latest/>

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P2OUT &= ∼0x08; // turn on green LED

while(P2IN&0x02);
while(!(P2IN&0x02));

P2OUT |= 0x08; // turn off green LED

P1OUT &= ∼0x80; // turn on yellow LED

while((P2IN&0x02));
while(!(P2IN&0x02));
}
}

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