ProblemwithPWMfrequency

**Darrel Taylor** · - 26th March 2012, 16:12

Code:

sineval var byte[36]
sineval[0] = 512    
sineval[1] = 583
...

The array should be of WORDs if you want it to hold values greater than 255.

PROTEUS Rules!!

**HenrikOlsson** · - 26th March 2012, 16:23

What Darrel said.

AND

In a post made March 13th:

You answered your own question in (1) from the Midrange manual:

(1) " If the PWM duty cycle value is longer than the PWM period, the CCPx pin will not be cleared. This allows a duty cycle of 100%".

Any dutycycle value above 796 will result in 100% dutycycle. In other words your SIN-output will be distorted/clipped.

You have several values larger than 796 (4*199 (which is what you have PR2 set to, remember we've been thru this)) in your lookuptable so you are "overdriving" the dutycycle register and "clipping" will occur.

/Henrik.

**sangaboy** · - 27th March 2012, 18:58

Hi to all
I tried to modify the code according to Darrel Taylor and HenrikOlsson comments but the problem still exits, let me put in real hardware and see what happen.
And here is modified code but the output is still like that posted in the previous post.

Code:

define OSC 4
Wsave var byte   $70system
Wsave1 var byte  $A0system
Wsave2 var byte  $120system
Wsave3 var byte  $1A0system

STEPCOUNT var byte
STEPCOUNT1 var byte

LED1   VAR  PORTB.1

STEPCOUNT = 0   'pointer for phase one in sinearray
STEPCOUNT1 = 12 'pointer for phase two  in sine array
ADCON0 = %00000000
ADCON1 = %00000000

TRISB = %11111101
TRISC = %11111001  'PMW output for CCP1 AND CCP2
TRISA = %11111111
TMR2 = 0
PR2 = 199 'generate 5khz  'set for 18Khz HPWM
CCP1CON = %00001100 'set CCP1 for PWM OPERATION
CCP2CON = %00001100 'set CCP2 for PWM OPERATION
T2CON = %00000100  'TIMER2ON and prescale of 1:1 

sineval var word[36]
sineval[0] = 512    
sineval[1] = 556   
sineval[2] = 599
sineval[3] = 640
sineval[4] = 676
sineval[5] = 707
sineval[6] = 733
sineval[7] = 752
sineval[8] = 763
sineval[9] = 767  
sineval[10] =763
sineval[11] =752
sineval[12] =733   
sineval[13] =707
sineval[14] =676
sineval[15] =640
sineval[16] =599
sineval[17] =556
sineval[18] =512   
sineval[19] =468
sineval[20] =425
sineval[21] =385 
sineval[22] =348
sineval[23] =317
sineval[24] =291
sineval[25] =272
sineval[26] =261
sineval[27] =257
sineval[28] =261 
sineval[29] =272
sineval[30] = 291
sineval[31] = 317
sineval[32] = 348
sineval[33] = 385
sineval[34] = 425
sineval[35] = 468

timerone var word 
Temp var byte
Temp1 var byte
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System          emp
'INCLUDE "ReEnterPBP.bas" 
 
ASM
 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM
 
T1CON = 000001                 ; Prescaler = 1;1, TMR1 ON
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts 
 
timerone =  65080' gives1818hz nterruptfrequency or about 50 htz sine 
Main:
       PAUSE 5
 
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------

sine:
     T1CON = 000000 'stop the timer

    TMR1L = timerone.byte0  'reload the timer
    TMR1H = timerone.byte1
    T1CON = 000001          ' start the timer
    
    
    TeMP = sineval[STEPCOUNT]
    CCP1CON.4 = Temp.0 ' bit 0
    CCP1CON.5 = Temp.1 ' bit 1       
    CCPR1L = Temp >>2  'Bit 2-7 
    
    TeMP1 = sineval[STEPCOUNT1]
    CCP2CON.4 = Temp1.0 ' bit 0
    CCP2CON.5 = Temp1.1 ' bit 1       
    CCPR2L = Temp1 >>2  'Bit 2-7
    TOGGLE LED1 
    stepcount =  stepcount +1
    stepcount1 =  stepcount1 +1
    
    if stepcount =36 then stepcount =0
    if stepcount1 =36 then stepcount1 =0
     
 
@    INT_RETURN

Thanks.

**sangaboy** · - 30th March 2012, 14:59

Hi to all
I try to download my program from my computer(wind7)using PIC16f877 development board and ET-CAB10PIN V2 interfacing cable but WHEN I try to run winpic800 software.
the following problems arise.
(1)failed to import Smport.sys
(2)when I check the hardware it say hardware not responding

any one can help me how to solve this problems
thanks

**Demon** · - 30th March 2012, 18:21

http://lmgtfy.com/?q=winpic800+failed+to+import

Robert

**sangaboy** · - 12th April 2012, 13:09

Hi every one
(1) Previous I thought that the problem of flat spot on my SPWM signal was due to the simulator(ISIS) but I was wrong because I implement it on the actual hardware using PIC16F877V1-V2 DEVELOPMENT BOARD board and DLIS40L oscilloscope but the problem still remain now I'm totally confused what cause that problem of flat spot to my wave form. I try to scale my look up table so that my dutycycle lie on the range of (0 to 4*199) but nothing was change to my signal
when viewed.
(2)ARE the ten bit look table is not working on 8bit chip like 16F877 0R 16F777 ? I think those values greater than 255 is one cause that problems

Code:

define OSC 4
Wsave var byte   $70system
Wsave1 var byte  $A0system
Wsave2 var byte  $120system
Wsave3 var byte  $1A0system
 
STEPCOUNT var byte
STEPCOUNT1 var byte
 
LED1   VAR  PORTB.1
 
STEPCOUNT = 0   'pointer for phase one in sinearray
STEPCOUNT1 = 12 'pointer for phase two  in sine array
ADCON0 = %00000000
ADCON1 = %00000000
 
TRISB = %11111101
TRISC = %11111001  'PMW output for CCP1 AND CCP2
TRISA = %11111111
TMR2 = 0
PR2 = 199 'generate 5khz  'set for 18Khz HPWM
CCP1CON = %00001100 'set CCP1 for PWM OPERATION
CCP2CON = %00001100 'set CCP2 for PWM OPERATION
T2CON = %00000100  'TIMER2ON and prescale of 1:1
 
sineval var word[36]
sineval[0] = 512   
sineval[1] = 556  
sineval[2] = 599
sineval[3] = 640
sineval[4] = 676
sineval[5] = 707
sineval[6] = 733
sineval[7] = 752
sineval[8] = 763
sineval[9] = 767 
sineval[10] =763
sineval[11] =752
sineval[12] =733  
sineval[13] =707
sineval[14] =676
sineval[15] =640
sineval[16] =599
sineval[17] =556
sineval[18] =512  
sineval[19] =468
sineval[20] =425
sineval[21] =385
sineval[22] =348
sineval[23] =317
sineval[24] =291
sineval[25] =272
sineval[26] =261
sineval[27] =257
sineval[28] =261
sineval[29] =272
sineval[30] = 291
sineval[31] = 317
sineval[32] = 348
sineval[33] = 385
sineval[34] = 425
sineval[35] = 468
 
timerone var word
Temp var byte
Temp1 var byte
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System          emp
INCLUDE "ReEnterPBP.bas"
 
ASM
 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM
 
T1CON = 000001                 ; Prescaler = 1;1, TMR1 ON
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts
 
timerone =  65080' gives1818hz nterruptfrequency or about 50 htz sine
Main:
       PAUSE 5
 
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------
 
sine:
     T1CON = 000000
 
    TMR1L = timerone.byte0 
    TMR1H = timerone.byte1
    T1CON = 000001         
   
   
    TeMP = sineval[STEPCOUNT]
    CCP1CON.4 = Temp.0 ' bit 0
    CCP1CON.5 = Temp.1 ' bit 1      
    CCPR1L = Temp >>2  'Bit 2-7
   
    TeMP1 = sineval[STEPCOUNT1]
    CCP2CON.4 = Temp1.0 ' bit 0
    CCP2CON.5 = Temp1.1 ' bit 1      
    CCPR2L = Temp1 >>2  'Bit 2-7
    TOGGLE LED1
    stepcount =  stepcount +1
    stepcount1 =  stepcount1 +1
   
    if stepcount =36 then stepcount =0
    if stepcount1 =36 then stepcount1 =0
    
 
@    INT_RETURN

(3) I'm not clear on the WINPIC800V358 software parameter on the attachment.

Any one can help me to solve these problems
Thankx