Double-edge triggered PWM

This notebook will be with information about a simple double-edge triggered PWM scheme.

By using double-edge triggered PWM it is possible to trigger one output for a specific time and then wait a while and then again trigger another output, and doing this again and again. I did this simply as I needed a PWM based H-bridge for my constant-current driver.

Have a look at the LPC1768 user manual for the registers

The code:

#include "mbed.h"

PwmOut myled(p23);
PwmOut myled2(p25);

int main()
    myled.period(1);        // Includes enables and magic stuff from the mbed side. 

// 24000 pr. ms in mr0 ie. 24 counts pr. uS in MR0 register. - Register manipulation
    LPC_PWM1->MR0 = 24*100;     // 100 usek routine / 10khz
    LPC_PWM1->MR1 = 0;          // set the pwm2 output high at this count
    LPC_PWM1->MR2 = 24*50;      // set the pwm2 output low at this count
    LPC_PWM1->MR3 = 24*50;      // set the pwm4 output high at this count
    LPC_PWM1->MR4 = 24*100;      // set the pwm4 output low at this count
    LPC_PWM1->MR5 = 24*66;      // Set PWM6 output high at this count
    LPC_PWM1->MR6 = 24*41;      // Set PWM6 output low at this count
    LPC_PWM1->PCR |= 0x14;      // 0x54 to include PWM6 output - PCR controls if the PWMs are single or double edge triggered
    LPC_PWM1->LER |= 0x1e;      // 0x7E to include PWM6 output for control - LER Latch enable register for latches between PWM outputs
    // Hereafter we do nothing at all with but while forever.
    while(1) {

This code will output a 50 percent square wave on pins p23 and p25. This can be changed with the registers. Look at the comments, you will get the idea (Phoo)....

If anyone want a library, and I have the time, I will go ahead and write one.


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