This code runs the Low Voltage Motor Booster Pack for the MSP-430 with the MSP430G2553 chip but could easily be adapted to any microcontroller. This uses Timer1_A0 to make a timing interrupt. Using the timing interrupt it changes the duty cycle of the PWM. Supports reverse by sending the “move_motors” command negative values.

Default is P2.0, P2.1, P2.2, and P2.3 for controlling the motor driver. P1.0 is toggled (on board LED) in the ISR.

Code: CCS V5

isr_motor_pwm.c
isr_motor_pwm.h
Project File Ver1.0

/*
*isr_motor_pwm.c
*Version: 1.0
*Parker Dillmann
*The Longhorn Engineer (c) 2013
*www.longhornengineer.com
*
*Check bottom of file for License.
*
*/

#include "msp430g2553.h"
#include "isr_motor_pwm.h"

#define Motor_DIR P2DIR
#define Motor_OUT P2OUT

#define Motor_A1 BIT0
#define Motor_A2 BIT1
#define Motor_B1 BIT2
#define Motor_B2 BIT3

volatile int Motor_Speed_A;
volatile int Motor_Speed_B;

volatile int Motor_isr_cnt;

void init_motors(void)
{
TA1CCTL0 = CCIE;             //Enable the CCR0 interrupt
TA1CCR0 = 50000;             // Set the interrupt register to "trip" each 50000 cycles"

TA1CTL = TASSEL_2 + MC_2 + TACLR;     //Timer_A Source Select; Set source to SMCLK, continuous mode, clear TAR

P1DIR |= 0x41;                            // P1.0 output

Motor_DIR |= (Motor_A1 | Motor_A2 | Motor_B1 | Motor_B2);    //Set Motors to output
Motor_OUT &= ~(Motor_A1 | Motor_A2 | Motor_B1 | Motor_B2);    //Set Motor outputs to 0

Motor_isr_cnt = 1;

return;
}

void move_motors(int Speed_A, int Speed_B)
{
Motor_Speed_A = Speed_A;
Motor_Speed_B = Speed_B;
return;
}

void stop_motors(void)
{
Motor_Speed_A = 0;
Motor_Speed_B = 0;
return;
}

#pragma vector = TIMER1_A0_VECTOR
__interrupt void Timer1_A0_ISR(void)
{
//Upkeep Time
Motor_isr_cnt++;
if (Motor_isr_cnt == 512)
{
Motor_isr_cnt = 1;
}

//Motor_A PWM
if (abs(Motor_Speed_A) >= Motor_isr_cnt)
{
if (Motor_Speed_A > 0)
{
Motor_OUT |= Motor_A1;
Motor_OUT &= ~(Motor_A2);
}
else
{
Motor_OUT |= Motor_A2;
Motor_OUT &= ~(Motor_A1);
}
}
else
{
Motor_OUT &= ~(Motor_A1 + Motor_A2);
}

//Motor_B PWM
if (abs(Motor_Speed_B) >= Motor_isr_cnt)
{
if (Motor_Speed_B > 0)
{
Motor_OUT |= Motor_B1;
Motor_OUT &= ~(Motor_B2);
}
else
{
Motor_OUT |= Motor_B2;
Motor_OUT &= ~(Motor_B1);
}
}
else
{
Motor_OUT &= ~(Motor_B1 + Motor_B2);
}

  P1OUT ^= 0x40;    // Toggle P1.0
TA1CCR0 += 500;  //Add offset to CCR0
}