Updating HPWM frequently, safe?

**mister_e** · - 6th May 2007, 00:50

first you'll have to match the calc values to suit your need. With your current code example (which seems to be one of mine, the calc will give you...
<IMG SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1593&stc=1&d=117840872 7">

look at this section of the code

Code:

        duty = 52                           ' duty value for 50% duty cycle
        PR2 = 25                            '
        T2CON = %00000100                   ' timer2 on, prescale 1:1
        CCPR1L = duty>>2                    ' MSB of duty cycle value
        CCP1CON=%00001100 | (dUTY<<5)       ' set PWM mode and store the 
                                            '   2 LSB of duty

52 is showned in the result section and it's to set the duty cycle to 50% as selected in the duty cyle section.

Now if you want to update the duty cycle, you could use this section

Code:

        CCPR1L = duty>>2                    ' MSB of duty cycle value
        CCP1CON=%00001100 | (dUTY<<5)       ' set PWM mode and store the 
                                            '   2 LSB of duty

in your code you just need to change the value of Duty variable.

The example was for a 16F877, you should have a look at the 12F683 to see if they work the same way.

post your whole code, maybe some register need to be set in a different way. I'll put some effort and open my datasheet as well

**peu** · - 6th May 2007, 00:55

it seems we posted at the same time, yes the post I used is from an old post of yours I used for reference. Please read my last post and tell if if you have an idea that may help me. Thanks!

**mister_e** · - 6th May 2007, 01:18

mm, you didn't disable the analog comparator.. maybe it worth to do it first?

i'm about to do something here to see what's happen.

**mister_e** · - 6th May 2007, 02:07

try this

Code:

<font color="#000000">        <font color="#008000">'
        '       Pic Configuration
        '       =================
        </font>@ __CONFIG _INTRC_OSC_NOCLKOUT &amp; _WDT_ON &amp; _PWRTE_ON &amp; _MCLRE_OFF &amp; _BOD_ON         
        
        <font color="#008000">'
        '       Hardware configuration
        '       ======================
                '
                '       I/Os
                '       ----
        </font>TRISIO = %00010010        
                <font color="#008000">'
                '       ADC's
                '       -----
        </font>ANSEL = %00000010  
        <font color="#000080">DEFINE </font>ADC_BITS 10     <font color="#008000">' ADCIN resolution  (Bits)
        </font><font color="#000080">DEFINE </font>ADC_CLOCK 1     <font color="#008000">' ADC clock source  (Fosc/8)
        </font><font color="#000080">DEFINE </font>ADC_SAMPLEUS 11 <font color="#008000">' ADC sampling time (uSec)                      
        </font>ADCON0.7 = 1           <font color="#008000">' Right justified results
     
                '
                '       Comparator
                '       ----------
        </font>CMCON0 = 7             <font color="#008000">' Disable comparator
        </font>VRCON = 0              <font color="#008000">' CVreff = OFF
                '
                '       CCP
                '       ---
                        '   PWM Freq=4KHz
                        '   Initial duty cycle set to 50%
                        '   PICMultiCalc says
                        '   10 Bit resolution when prescaler = 1:1
                        '   MAX duty value 1000
                        '   PR2 = 249
        </font>CCP1CON = %00001100     <font color="#008000">' PWM mode
        </font>PR2 = 249               <font color="#008000">'         
        </font>T2CON = %00000100       <font color="#008000">' Start Timer2, Prescaller 1:1
      
        '   
        '       Software variables
        '       ==================
        </font>Duty    <font color="#000080">VAR WORD
        
        </font><font color="#008000">'
        '       Software constants
        '       ==================
        </font>PWM_ON  <font color="#000080">CON </font>%00001100
        PWM_OFF <font color="#000080">CON </font>0
        
        <font color="#008000">'
        '       Software/Hardware initialisation
        '       ================================
        </font>GPIO = 0
        <font color="#000080">PAUSE </font>50    <font color="#008000">' OSC settle delay
        </font>Duty = 0
        <font color="#000080">GOSUB </font>SetPWMDuty
        
        <font color="#008000">'------------------------------&lt; Main program &gt;-----------------------------------
        '
</font>Start:
        <font color="#000080">ADCIN </font>1,Duty                    <font color="#008000">' read pot
        </font><font color="#000080">IF </font>Duty&gt;1000 <font color="#000080">THEN </font>Duty =1000    <font color="#008000">' avoid results &gt;1000
        </font><font color="#000080">GOSUB </font>SetPWMDuty                <font color="#008000">' Set PWM duty cycles
        </font><font color="#000080">PAUSE </font>1                         <font color="#008000">' allow few PWM cycles
        </font><font color="#000080">GOTO </font>Start
        <font color="#008000">'
        '---------------------------------------------------------------------------------

        '-------------------------------&lt; Subroutines &gt;-----------------------------------
        '
</font>SetPWMDuty:
        <font color="#008000">'       Datasheet recommend to stop PWM, load duty cycles vale
        '       to avoid possible glitches.
        '
                '
                '       stop PWM
                '       --------
        </font>CCP1CON = PWM_OFF  
                <font color="#008000">'
                '       load Duty values
                '       ----------------
        </font>CCPR1L = Duty &gt;&gt;2   
        CCP1CON.5 = Duty.1
        CCP1CON.4 = Duty.0
                <font color="#008000">'
                '       Start PWM
                '       ---------
        </font>CCP1CON = CCP1CON | PWM_ON              
        <font color="#000080">RETURN
        </font><font color="#008000">'
        '---------------------------------------------------------------------------------
</font>

things to remember, disable the PWM mode, update the duty cycle, start PWM mode and allow few PWM freq cycle.. unless results could be weird.