3 channel PWM with customize duty cycle

[photoelectric]

Hi ppl,

im working on my PIC basic pro project to generate 3 channel pwm using PIC 16f737 family and i found some coding from previous thread. i test it and it works well.
but the PWM generated used fixed value of duty cycle and i want to change into customize duty cycle by using lookup command in PICBAsic pro .

my lookup table is below:

For DUTY1 = 0 TO 44

LookUp DUTY1, [0,18,35,53,70,87,104,120,135,150,164,177,190,201,2 11,221,229,236,_
243,247,251,254,255,254,251,247,243,236,229,221,21 1,201,189,_
177,164,150,135,120,104,87,70,53,35,18,0],DUTY2

next DUTY1

and here is my 3 channel coding:

ClearWDT

DEFINE OSC 20
' Word vars for 10-bit value of each PWM duty cycle
Duty1 VAR WORD ' Channel #1
Duty2 VAR WORD ' #2
Duty3 VAR WORD ' #3

' Set CCPx pins to outputs
TRISC.2=0 ' CCP1 output
TRISC.1=0 ' CCP2 output (could also be assigned to RB3)
TRISB.5=0 ' CCP3 output

' Set CCP modules to PWM mode
CCP1CON = %00001100 ' Mode select = PWM
CCP2CON = %00001100 ' Mode select = PWM
CCP3CON = %00001100 ' Mode select = PWM

' Set period up for 1.22kHz PWM freq
PR2 = 249

' Set TMR2 up for 1:16 prescale & turn it on
T2CON = %00010101 ' TMR2 ON 1:16 prescale

Duty1 = 512 ' 50% duty cycle. 1024/2 "10-bit resolution"
CCP1CON.4 = Duty1.0 ' Setup 10-bit duty cycle as
CCP1CON.5 = Duty1.1 ' a 10-bit word
CCPR1L = Duty1 >> 2

Duty2 = 512
CCP2CON.4 = Duty2.0
CCP2CON.5 = Duty2.1
CCPR2L = Duty2 >> 2

Duty3 = 512
CCP3CON.4 = Duty3.0
CCP3CON.5 = Duty3.1
CCPR3L = Duty3 >> 2

End

and my problem is i cannot combine the lookup command and the 3channel coding to generate the customize duty cycle ??
can any1 help explaning how?

thanks
photoelectric

[HenrikOlsson]

Hi,
Well, if you have the lookup-table in a for-next loop like you are currently showing it will run thru that loop and then continue with the reset of the code. You have to move the NEXT so that it actually updates the dutycycles registers with the value retreived from the table before looking up the next value.

For duty = 0 to 44
Lookup.....
Set dutycycle
Pause whatever
Next

Then, in order to get you three phases you either need to have three lookup tables or you need to index the same lookuptable by offsetting the index by 1/3 for each phase and keep track of when to "roll over" and start at 0 again for each phase.

[photoelectric]

hi henrik, thanks for explaining.
but i ve try ur method using below coding for 1 channel but the the output ccp wont work. its doesnt come out the correct dutycyle from the lookup table for my PWM.
below are the example of my coding:

For DUTY1 = 0 TO 44

LookUp DUTY1, [0,18,35,53,70,87,104,120,135,150,164,177,190,201,2 11,221,229,236,_
243,247,251,254,255,254,251,247,243,236,229,221,21 1,201,189,_
177,164,150,135,120,104,87,70,53,35,18,0],DUTY2

Duty1 = DUTY2 ' 50% duty cycle. 1024/2 "10-bit resolution"
CCP1CON.4 = Duty1.0 ' Setup 10-bit duty cycle as
CCP1CON.5 = Duty1.1 ' a 10-bit word
CCPR1L = Duty1 >> 2
next DUTY1

you see i declare the DUTY1 = DUTY2 for my dutycycle but it wont work


please help assist.

thanks

[HenrikOlsson]

Hi,
You have Duty1 as the "index" for the lookup table. Duty1 is therefor expected to count 0, 1, 2, 3, 4...44 but you are overwriting Duty1 with the value of Duty2 so the indexing (the for-next loop) wont work properly.

Use Duty2 directly when setting the dutycycle register or use another variable for indexing the lookup table (and don't overwrite it in the middle of the loop).

/Henrik.

[photoelectric]

hi,

yes i got your point now and correcting my coding now but then i realize how to define my dutycycle value from the lookup above since dutycyle register only accept numbers. example

For DUTY1 = 0 TO 44

LookUp DUTY1, [0,18,35,53,70,87,104,120,135,150,164,177,190,201,2 11,221,229,236,_
243,247,251,254,255,254,251,247,243,236,229,221,21 1,201,189,_
177,164,150,135,120,104,87,70,53,35,18,0],DUTY2

Duty2 = ?????? ' duty cycle. 1024/2 "10-bit resolution"
CCP1CON.4 = Duty1.0 ' Setup 10-bit duty cycle as
CCP1CON.5 = Duty1.1 ' a 10-bit word
CCPR1L = Duty1 >> 2
next DUTY1

what should i define the duty2 value since i want it to read from lookup table?

photoelectric

[photoelectric]

hi,

yes i got your point now and correcting my coding now but then i realize how to define my dutycycle value from the lookup above since dutycyle register only accept numbers. example

For DUTY1 = 0 TO 44

LookUp DUTY1, [0,18,35,53,70,87,104,120,135,150,164,177,190,201,2 11,221,229,236,_
243,247,251,254,255,254,251,247,243,236,229,221,21 1,201,189,_
177,164,150,135,120,104,87,70,53,35,18,0],DUTY2

Duty2 = ?????? ' duty cycle. 1024/2 "10-bit resolution"
CCP1CON.4 = Duty2.0 ' Setup 10-bit duty cycle as
CCP1CON.5 = Duty2.1 ' a 10-bit word
CCPR1L = Duty2 >> 2
next DUTY1

what should i define the duty2 value since i want it to read from lookup table?

photoelectric

[HenrikOlsson]

Duty2 already contains the value from the lookuptable - that is what your Lookup does, it assignes the value pointed at by Duty1 to the variable Duty2 in this case.

For each iteration thru the loop Duty2 will contain the value pointed at by Duty1 and since Duty1 counts 0,1,2,3...44 Duty2 will contain 0,18,35,53...0

/Henrik.