6 HPWM signal generation with PIC18F4431

[HenrikOlsson]

Hi,
Yes, it's probably a timer problem. You have TMR1 set up to derive its clock from the main oscillator (Fosc/4) so 10Mhz in your case. (Your code comments says you have a prescaler of 8 but you don't - it's 1:1.

TMR1 is a 16bit timer and generates an interrupt when it overflows from $FFFF to $0000. In your case this means that the interrupt frequency is 10MHz/65536 = 152.6Hz. In other words, the pwmint interrupt service routine is executed 156 times per second.

If a complete sinus cycle consists of 256 "steps" you should get a frequency of 152.6/256=0.6Hz but you claim 0.25Hz so I'm not sure what's going on exactly.

If you want to speed up the frequency you must increase the interrupt frequency. You do this by preloading TMR1 in the interrupt service routine so that it doesn't have to count all the way from 0. If you, for example, preset it to 32768 you'll get twice as many interrupts per second as when letting it free run.

/Henrik.

[pxidr84]

Thanks Henrik, now I use TMR1L and TMR1H registers, I got a 40 Hz sine (it's better).

I've heavly modified the code, I didn't use the SIN function anymore, but a lookup table with 72 values (5 degrees/value).

Now, for debugging, I want to vary the timer value. For that, I use two buttons, one for increase (PORTC.4), one for decrease (PORTC.5), and then display the value to my LCD.

The LCD works fine, but not the inputs. If I push the buttons, nothing happens. No increase or decrease. Same thing in the simulator.

My code :

' PIC initialization
DEFINE OSC 40      
DEFINE LCD_DREG PORTC
DEFINE LCD_EREG PORTD
DEFINE LCD_RSREG PORTD
DEFINE LCD_EBIT 0
DEFINE LCD_RSBIT 1
DEFINE LCD_COMMANDUS 10000
DEFINE LCD_DATAUS 1000 


' BAS includes
INCLUDE "DT_INTS-18.bas"
INCLUDE "Sine_table.bas"


' Port registers configuration
TRISB=%11000000   ' PWM 0,1,2,3,4,5 outputs
TRISC=%00110000   ' +/- buttons

' PCPWM registers configuration
DTCON=%110        ' Deadtime (600ns)
PTCON0=%0         ' 1:1 postscale, Fosc/4 1:1 prescale, free running mode
PTCON1=%10000000  ' PWM time base is ON, counts up, 19.45kHz/4
PWMCON0=%1000000  ' PWM 0,1,2,3,4,5 set in pair mode
PWMCON1=%1        ' PWM timer sync configuration


' PWM calculation variables
ustep var byte
vstep var byte
wstep var byte
uduty var word
vduty var word
wduty var word
timer var word
amplitude var word
carrier VAR word


' Variables definition
ustep=72          ' 360 degrees phase angle
vstep=48          ' 240 degrees phase angle
wstep=24          ' 120 degrees phase angle
timer=60950       ' Frequency adjust (60950=80Hz) 
amplitude=65535   ' Sinewave amplitude adjust (65535=max amplitude)
carrier=1023      ' Carrier frequency adjust (1023=13kHz)
  

' PWM carrier frequency register configuration
PTPERL=carrier.lowbyte  
PTPERH=carrier.highbyte


' Inverter startup
pause 2000
Lcdout $FE,1 
LCDOUT $FE,2,"Varidrive 1.0"
LCDOUT $FE,$C0,"DR Electronique"
pause 2000
  
  
' Interrupt processor 
ASM
INT_LIST  macro
        INT_Handler   TMR1_INT,   _pwmint,   ASM,  yes
    endm
    INT_CREATE
ENDASM
 
        
' Timer configuration
T1CON=%1           
@ INT_ENABLE  TMR1_INT   


test var word
test=1


' Main program loop
mainlp:

' Debug display
LCDOUT $FE,1
LCDOUT $FE,2,"Timer var :"
LCDOUT $FE,$C0,#test

if PORTC.4=1 then test=test-1
if PORTC.5=1 then test=test+1
pause 100

goto mainlp


' PWM calculation and update interrupt 
pwmint:

' Sinewaves frequency
TMR1L=timer.lowbyte
TMR1H=timer.highbyte

' PWM U phase calculation
uduty=sine[ustep]
uduty=uduty<<4**amplitude

' PWM V phase calculation
vduty=sine[vstep]
vduty=vduty<<4**amplitude

' PWM W phase calculation
wduty=sine[wstep]
wduty=wduty<<4**amplitude

' PWM U, V and W update
PDC0L=uduty.lowbyte
PDC0H=uduty.highbyte
PDC1L=vduty.lowbyte
PDC1H=vduty.highbyte
PDC2L=wduty.lowbyte
PDC2H=wduty.highbyte

' Phase angle calculation
ustep=ustep-1
vstep=vstep-1
wstep=wstep-1
    
' Phase angle reinitialization
if ustep=0 then ustep=72
if vstep=0 then vstep=72
if wstep=0 then wstep=72
 
@ INT_RETURN

The faulty code is in bold.

[pxidr84]

Problem resolved, I will open a new thread.

[oswalam]

hello, i am new to this forum, I am final year electrical engg. student, my project is 'Speed control of Induction motor using PCPWM in PIC18f4431'. Plz guide me how to go about it, i want to write a code for sinusoidal PWM generation using PCPWM in edge aligned mode.