Freescale's PWM output controls the direction of the servo motor

1. Servo motor. When the PWM output cycle is within a certain range, the steering direction of the servo will be proportional to the PWM duty cycle.
2. PWM output of HCS12.
Solution:
1. The PWM module in HCS12 performs PWM output through hardware.
2. The comparison output module of ECT in HCS12 performs PWM output through comparison output.
Since the PWM module is a dedicated module for output PWM, PWM output can be achieved by setting the corresponding registers, which is simple, convenient and accurate. Therefore, the PWM module is selected for PWM output.
Description:
1. The steering angle of the servo is controlled by PWM. The servo interface generally has 3 wires, black ground wire and red power wire, generally using 4.8V and 6V standards. The other wire is the control signal line.
2. 16-bit PWM output is achieved through cascading.
3. The cycle is 18MS~20MS, that is, the output cycle is 56Hz~50Hz.
4. The alignment method is PWM left alignment.
5. The output polarity is the starting high level.
6. The pulse width varies from 1100us to 1900us, achieving a steering angle of -45° to 45°.
7. Achieve 16-bit PWM output through cascading. Channel PWM45 forms channel A.
8. Clock source selection.
  BusBlock: 24MHz.
  void pllclk(void) //24MHz
  {
      SYNR=0x02;     //PLLCLK =2*OSCCLK*(SYNR + 1)/(REFDV + 1)
      REFDV=0x01;
      CLKSEL=0x80;   //Select PLL clock
  }
9. PWM clock.
  Channel clock period 2us
  Output period 20MS
  PWM output frequency: 50Hz.
  Pre-division: 8-division     3MHz
  PWMPRCLK=0x66
  Division: 6-division 500kHz
  ClockSX=ClockX/(2*PWMSCLX)
  PWMSCLx=ClockX/ClockSX*2=3M/(500k*2)=3=0x03
  Through two divisions, the channel clock period is: 100US, i.e. 10KHZ
  Channel A clock frequency selects PWMPRCLK and PWMSCLA;
  Channel B clock frequency selects PWMPRCLK and PWMSCLB;
  Period calculation formula:
  Left alignment:
    Output period = channel clock period * (PWMPERx+1)
    PWMPERx=output period/channel clock period-1
    =20MS/2us-1
    =9999=0x270f
10. Duty cycle setting:
  Left alignment starts with output high level:
  Duty cycle = [(PWMDTYx+1)/(PWMPERx+1)]*100%
  PWMDTYx=duty cycle*(PWMPERx+1)/100%
According to the formula:
[(PWMDTYx+1)/(PWMPERx+1)]*100%=pulse width/output period*100%
  PWMDTYx=(pulse width*PWMPERx)/output period-1
        =(pulse width*9999)20000-1Pulse

width=rotation angle*(400)/45+1500   (us)
  Through the loop, the PWMDTx value corresponding to the rotation angle of the servo motor can be calculated.
PWMDTYx[28]={859,855,850,846,841,837,832,828,824,819,815,810,806,801,797,792,788,784,779,775,
770,766,761,757,752,748,744,740,735,731,726,722,717,713,708,704,700,695,691,686,
682,677,673,668,664,660,655,651,646,642,637}
The program to calculate the PWMDTYx value is as follows:
#include
void main()
{
long int i,X,y; } } CODE
: #include <  hidef.h  > #include  < 
MC9S12XS128.h >  #pragma LINK_INFO  DERIVATIVE  " mc9s12xs128 " // =========================================================== // //16-bit PWM output controls the rotation of the servo motor //author: yangtze //time:2009/4/21/ //==============================================================// #define PWMPERx  0x270F; unsigned int PWMDTYxtable[]={
 
  
      
  




     
   







 

0x035b,0x0357,0x0352,0x034e,0x0349,0x0345,
0x0340,0x033c,0x0338,0x0333,0x032f,0x032a,
0x0326,0x0321,0x031d,0x0318,0x0314,0 x0310,
0x030b,0x0307,0x0302,0x02fe,0x02f9,0x02f5,
0x02f0, 0x02ec,0x02e8,0x02e4,0x02df,0x02db,
0x02d6,0x02d2,0x02cd,0x02c9,0x02c4,0x02c0,
​​0x02bc,0x02b7,0x02b3,0x02ae,0x02aa,0x02a5,
0x02a1,0x029c,0x0298,0x0294,0x028f,0x 028b,
0x0286,0x0282,0x027d};
void pllclk(void)// 24MHz
{
  SYNR=0x02;     //PLLCLK =2*OSCCLK*(SYNR + 1)/(REFDV + 1)
  REFDV=0x01;
  CLKSEL=0x80;   //Selected PLL clock
}
  
  
void PWMServoMotor_init(void) //PWM initialization settings
{
  PWMPRCLK=0X66; //Set channel period
  PWMSCLA=0X03;
  PWMSCLB=0X03;
  PWMCLK=0XFF;
  
  PWMPOL=0X00; //Start output high level
  PWMCAE=0X00; // Waveform left-aligned
  PWMCTL=0XFC; //Select cascade output
}

void PWM_Pulse(unsigned int PWMPERx,unsigned int PWMDTYx) //PWM output period and duty cycle setting
{
    PWMPERH=(PWMPERx>>8)&0X00FF;
    PWMPERL=PWMPERx&0X00FF ;
    
    PWMPER4=PWMPERH;   //Set the output period
    PWMPER5=PWMPERL;
    
    PWMDTYH=(PWMDTYx>>8)&0X00FF;
    PWMDTYL=PWMDYx&0X00FF;
    
    PWMDTY4=PWMDTYH;   //Set pulse width
    PWMDTY5=PWMDTYL;
    
    PWME=0X18; //Channel 45 is enabled
}
void main(void)
{
  unsigned int PWMDTYx;
  PWMDTYx=PWMDTYxtable[5];
  pllclk();
  PWMServoMotor_init();
  PWM_Pulse(PWMPERx,PWMDTYx);
  
  EnableInterrupts;
  for(;;) {}
  
}

      //Last time I wrote a program for driving a DC motor, I originally used 16-bit PWM modulation, but in the end I only used 8-bit. The second time I used the PWM module, I carefully studied the usage of this module and found that the biggest difference between 16-bit and 8-bit is not the length of the cycle or the size of the duty cycle. The biggest impact is the modulation accuracy. The larger the number of bits, the smaller the channel period that can be set, so that the set period and duty cycle can be more accurate. Large output cycle.