Help needed. To generate PWM on a freescale microcontroller

[Ram_newbee]

Hi all

Am using Freescale Micro controller MC9S08SH8. Iam trying to create a PWM using this controller. Though I have carefully set all the registers related to PWM, Am still unable to generate PWM on this.

The main task was to create a edge aligned PWM on all channels of each PWM.
also am using internal oscillator it has.

Can any one give me some example C Codes for the same or try correcting my code.

Tools am using: Codewarrior suite with P&E Programmer
Controller: MC9S08SH8 20pin


Any kind of help is greatly appreciated

Thanks!

My Code

#include <hidef.h> /* for EnableInterrupts macro */#include "derivative.h" /* include peripheral declarations */void main(void) {  EnableInterrupts; /* enable interrupts */     //TIMER1 CH0 n CH1          TPM1SC=0b01001000;     TPM1C0SC=0b00101000;  //Edge aligned pwm with high true pulses      TPM1C1SC=0b00101000;      TPM1MOD=400;     TPM1C0V=400;     TPM1C1V=400;          //TIMER2 CH0 n CH1        TPM2SC=0b01001000;     TPM2C1SC=0b00100100; //Edge aligned pwm with low true pulses      TPM2C0SC=0b00100100;     TPM2MOD=400;     TPM2C1V=400;     TPM2C0V=400;while(1){TPM1C0V=300;TPM1C1V=300;TPM2C1V=300;TPM2C0V=300;}   }

[bigmac]

Hello, and welcome to the forum.

I have successfully used the assembly equivalent of the following code to generate antiphase PWM signals to directly drive a piezo buzzer device.  The code was tested on a '9S08SE8, but should also work for the device you are using.

// TPM1 MODULE:// Generates 4 kHz PWM push-pull output from Ch0 and Ch1 for piezo.// Overflow period: 250 us#ifdef  LOW_TRIM#define TPM1MODval  999     //(1) (250*4.00 - 1)  4.00 MHz bus#else#define TPM1MODval  1249    //(2) (250*5.00 - 1)  5.00 MHz bus#endif#define TPM1SCval   0x08 /* 0b00001000  TPM1SC register                              |||||+++- PS     Prescaler divisor 1                              |||++---- CLKS   Bus rate clock                              ||+------ CPWMS  Edge aligned PWM mode                              |+------- TOIE   No overflow interrupt                              +-------- TOF    Read only flagNote: Clearing TPM1SC register will disable TPM1 module*/#define TPM1C0SCval 0x28 /* 0b00101000  TPM1C0SC register                              ||||++--- ELS0    High true output pulses                              ||++----- MS0     PWM mode (edge aligned)                              |+------- CH0IE   No channel interrupt                              +-------- CH0F    Read only flag*/#define TPM1C1SCval 0x2C /* 0b00101100  TPM1C1SC register                              ||||++--- ELS1    Low true output pulses                              ||++----- MS1     PWM mode (edge aligned)                              |+------- CH1IE   No channel interrupt                              +-------- CH1F    Read only flagNote: Clearing TPM1CnSC register will disable PWM output*//***************************************************************/// TPM1 module initialisationvoid TPM1_init( void){   TPM1MOD = TPM1MODval;   TPM1SC  = 0;             // Initially disable module}/***************************************************************/// TURN AUDIBLE BEEP ON/OFF#define DUTY_50   (TPM1MODval+1)/2 // PWM duty cycle 50%void BUZZ_ON( void){   TPM1SC   = TPM1SCval;    // Enable TPM1 module   TPM1C0SC = TPM1C0SCval;  // Enable TPM1 output Ch0   TPM1C1SC = TPM1C1SCval;  // Enable TPM1 output Ch1   TPM1C0V  = DUTY_50;      // PWM duty cycle 50%   TPM1C1V  = DUTY_50;      // PWM duty cycle 50%}void BUZZ_OFF( void){   TPM1C0SC = 0;   TPM1C1SC = 0;}

Regards,

Mac

[bigmac]

Hello,

I discovered that the code I previously posted was from an early version of the firmware.  The later version is different, presumably because of problems experienced during debugging.  Only the BUZZ_ON() function is affected, and the modified code follows.

void BUZZ_ON( void){   TPM1SC   = 0;            // Disable TPM1 module   TPM1C0V  = DUTY_50;      // PWM duty cycle 50%   TPM1C1V  = DUTY_50;      // PWM duty cycle 50%   TPM1SC   = TPM1SCval;    // Enable TPM1 module   TPM1C0SC = TPM1C0SCval;  // Enable TPM1 output Ch0   TPM1C1SC = TPM1C1SCval;  // Enable TPM1 output Ch1}

I now recall that the channel register settings did not update unless the TPM module was first disabled.  I apologise for any confusion.

Regards,

Mac

[Ram_newbee]

Hey thanks again for the update. I have changed the code to suit my prupose and since I dont need to use it for buzzer, I didn't encounter any problem. I have a few basic doubts.

What does this do?

#ifdef  LOW_TRIM
#define TPM1MODval  999     //(1) (250*4.00 - 1)  4.00 MHz bus
#else
#define TPM1MODval  1249    //(2) (250*5.00 - 1)  5.00 MHz bus
#endif

And also How can I generate PWMs with various frequencies. I mean what register should I vary if I have to change the frequency of my PWM.

Thanks!

[bigmac]

Hello,

The PWM period is determined by the modulo setting, within the TPMxMOD register.  Assuming the TPM module clock is sourced from the bus, and usually with a prescaler division by 1 for PWM, the number of bus cycles per PWM period will be one more than the modulo value.

The purpose of the preprocessor conditional #defines is to allow for PWM period calibration, in this case for a 250 microseconds period, for two different trim settings associated with the internal reference of the ICS module (using FEI mode).

Regards,

Mac

[Ram_newbee]

Thank You bigmac, I ll try to work it out and will update you accordingly

Regards