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Introduction to Programming the MSP430

Module by: adrian valenzuela. E-mail the author

Summary: This is a basic tutorial on how to program the basic digital peripherals on the MSP430 on the MSP430F16x Lite Development Board.

Configuring Digital I/O

Digital I/O such as the LEDs and pushbuttons are configured by modifying a several registers pertaining to the port that they are attached to. Check the datasheet to find 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.

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 number will correspond the to x value in registers such as PxIN, PxOUT, or PxDIR. Therefore, if we wanted to define the direction of a pin on port 2 we would write to P2DIR.

Exercise 1

How do we switch the three pins (P1.7, P2.2, and P2.3) corresponding to the LEDs to be outputs?

[ Show Solution ]

Output pins may be toggled using the PxOUT register. LEDs are turned on by setting their corresponding register bits low.

Exercise 2

How would be turn on the three LEDs without modifying any other bits in the register?

[ Show Solution ]

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 modified.

Exercise 3

Write a couple different polling schemes for detecting if BUTTON_1 was pushed.

Note:

PxIN bits corresponding to the push buttons are high by default (i.e. the button is not depressed.)

[ Show Solution ]

Exercise 4

Now we will write a program that lights up one of the LEDs and will light up a different 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 file by adding the following line at the top of the main.c file. 

#include <msp430x16x.h>

It may be helpful to define some macros for commonly used register values. For example, if we add #define red_on ~0x04 to the top of the file (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 off.

Complete the program.

[ Show Solution ]

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