basic.c

PWM Generation Using HCS12 Timer Channels

/******************************************************************************
* 		                                         COPYRIGHT (c) MOTOROLA 2003
* FILE NAME: basic.c                                                      
*                                                                           
* PURPOSE: demonstration program for PWM generation using timer module.											 
*                                                                           
* DOCUMENTATION SOURCE: EKB Applications                                         
*                                                                           
* TARGET DEVICE: MC9S12C32                                                                                                                                                                                                                                                                                            
*                                                                          
* COMPILER: Metrowerks                    					 VERSION: MOT_V3.0                                                                                        
*                                                                         
* AUTHOR: G.More/M.Gallop       LOCATION: EKB	      LAST EDIT DATE: 1/10/03
*                                                                         
* UPDATE HISTORY                                                         
* REV      AUTHOR       	DATE       DESCRIPTION OF CHANGE                  
* ---      ------       	--------   ---------------------                 
* 1.0      G.More/M.Gallop 	25/03/03   Initial Coding 	
* 2.0      G.More           1/10/03    Simple PWM generation example.   		                               
*
******************************************************************************/                                                                        
/*===========================================================================*/
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/*****************************************************************************/

#define BUSCLOCK_KHZ 24000 		/* use care! this value is used to calibrate PWM */
#define TIMERPRESCALER 1

/* include files */
#include "basic.h"

/* global variables */
unsigned long Period[1] = 0,  Mark[1] = 0, Space[1] = 0;	

/******************************************************************************
Function Name	:	main
Engineer		:	G.More / M.Gallop
Date			:	25/03/03
Parameters		:	NONE
Returns			:	NONE
Notes			:	main routine 
******************************************************************************/
void
main(void) 
{
	Pim.perh.byte = (PERH7);	/* set pull up devices on port H pin 7 */

	SetPLL(6,4);		/* configures bus clock at 24MHz using PLL - !needs correct loop filter components fitted! */
	ConfigureTimer();	/* calls timer setup routine */

	ConfigureChannel(0,50,125);	/* set up channel 0 for 50% duty and 125kHz clock */ 

	EnableInterrupts;	/* clear CCR interrupt mask */
	
	while(1)			/* forever loop */
	{
		if((Pim.pth.bit.pth7 == 1) && (Timer.tie.bit.c0i == 0))	/* if control signal = enable and timer is disabled */	
		{
				/* start generating PWM then hand over to ISR */
			Timer.tc[0].word = (Timer.tcnt.word + 10);	/* set up timer compare for known latency */
			Timer.tctl2.bit.ol0 = 1; 	/* set pin action to rising edge on first compare */
			Timer.tie.bit.c0i = 1;     	/* enable interrupt for this timer channel */    
		}
	}
}

/******************************************************************************
Function Name	:	ConfigureChannels
Engineer		:	G.More / M.Gallop
Date			:	25/03/03
Parameters		:	dutyCycle (percentage), frequency (kHz), channel
Returns			:	
Notes			:   beware of frequency limitations in relation to BUSCLOCK and
					TIMERPRESCALER value (may overflow 16-bit variable). No error
					checking is implemented in this function.
******************************************************************************/
void ConfigureChannel (tU08 channel, tU08 dutyCycle, tU16 frequency_khz)
{
	Period[channel] = ((BUSCLOCK_KHZ / TIMERPRESCALER) / frequency_khz); 
	Mark[channel] = ((Period[channel] * dutyCycle ) / 100);
	Space[channel] = (Period[channel] - Mark[channel]);
}

/******************************************************************************
Function Name	:	SetPLL
Engineer		:	A.McKechan / G.More	/ C.Culshaw	
Date			:	31/5/00
Parameters		:	multiplier, divider
Returns			:	NONE
******************************************************************************/
void SetPLL(tU08 multiplier, tU08 divider)
{
  	Crg.clksel.bit.pllsel = 0;			/* select crystal as bus clock */
  
  	if(!multiplier && !divider)			/* if multiplier and divider are 0 */		
    {
    	Crg.synr.byte = 0;				/* set synr (multiplier) to 0 */
    	Crg.refdv.byte = 0;				/* set refdv (divider) to 0 */
    	Crg.pllctl.bit.pllon = 0;    	/* turn PLL off */
    }
  	else
    {
    	Crg.pllctl.bit.pllon = 1;  		/* turn on the PLL */
	    Crg.synr.byte = multiplier-1;	/* set synr (multiplier) */
    	Crg.refdv.byte = divider-1;		/* set refdv (divider) */

	    while(!Crg.crgflg.bit.lock)		/* wait for PLL to lock */
     	{
     	}
    	Crg.clksel.bit.pllsel = 1;		/* select the PLL as the bus clock */
    }
}

/******************************************************************************
Function Name	:	ConfigureTimer
Engineer		:	G.More / M.Gallop
Date			:	25/03/03
Parameters		:	NONE
Returns			:	NONE
Notes			:	sets up the timer for one channel of PWM output.
******************************************************************************/
void 
ConfigureTimer(void)					
{
	Timer.tios.byte = (IOS0);			/* set channel one as output compare */
	Timer.tctl2.byte = (OM0);			/* set mode to follow output level bit */
	Timer.tscr2.byte = (TIMERPRESCALER);	/* set the prescaler to 0 - use care! */
	Timer.tscr1.byte = (TEN|TFFCA);		/* enable timer and set fast flags clear all */
}  
	
/*****************************************************************************/
/* Start of interrupt service routines  */
/* placed into non-banked memory segment as vectors are only 2 bytes */

#pragma CODE_SEG NON_BANKED	
/******************************************************************************
Function Name	:	_TimerCompare0ISR
Engineer		:	G.More / M.Gallop	
Date			:	25/03/03
Parameters		:	NONE
Returns			:	NONE
******************************************************************************/
#pragma TRAP_PROC
void 
_TimerCompare0ISR(void)
{
  	if (Timer.tctl2.bit.ol0 == 1) 		/* if channel is set to generate rising edge */
	{
		Timer.tc[0].word += Mark[0];	/* set up timer compare for mark time */
		Timer.tctl2.bit.ol0 = 0;		/* set pin action to falling edge */
		
		/* disable here to drive low on PWM stop */
		if (Pim.pth.bit.pth7 != 1)		/* if control signal = disable */
		{
			Timer.tie.bit.c0i = 0;  	/* disable interrupt */
		}
	}
	else
	{
		Timer.tc[0].word += Space[0];	/* set up timer compare for space time */
		Timer.tctl2.bit.ol0 = 1; 		/* set pin action to rising edge */

		/* disable here to drive high on PWM stop */	
	}                          
}

/******************************************************************************
Function Name	:	_dummyISR
Engineer		:	M.Gallop
Date			:	31/5/00
Parameters		:	NONE
Returns			:	NONE
******************************************************************************/
#pragma TRAP_PROC
void 
_dummyISR( void )
{
    while(1)	/* endless loop */
	{;
	}                                 
}

/* End of interrupt service routines  */
/* reset code segment to default */
#pragma CODE_SEG DEFAULT