Power Control PWM, HELP needed

[Kloney]

I added a "1 us" delay and it worked quite well but the wave took longer duration time, the output frequency is 16.6hz instead of 50hz becaus of the delay
I'm using 25 entry and the output should be 50hz (Fpwm = 50 * 25 = 1250 I guess ?) how can I fix that ?
Also for the DTCON I can't get this part I need a 5us dead-time and I'm using (Fosc/4) settings what are the calculations needed for "5-0" bits in DTCON to set such a dead-time ?

For Bruce's Example this is the part I'm talking about :

Duty = 800 ' ~50% PDC2L = Duty.LowByte ' maintain a fixed 50% duty cycle on PWM4,5 PDC2H = Duty.HighByte
But i don't think that I'm going to need that in my case I just was wondering to understand the whole thing what are the LowByte and HighByte ?

Thanks Henrick , I can't find words to describe how much you helped me

[HenrikOlsson]

Hi,
I suspect you added 1ms delay, not 1us.
Correct, if the table is 25 entries for a full cycle and you want 50Hz output you need to index the table at 1250Hz. The delay between each update of the dutycycle should then be 1/1250=800us (so use PauseUs 800 and see what happens). Then, of course, the actual updating of the dutycycle registers takes some small amount of time so if it's critical you'll need to tweak the delay.

The first and last entry in your "lookup table" are one and the same ($1000) - you'll get a "flat spot" in the cycle.

Ah, OK, now I see what you're asking....Bruce is not multiplying anything.
He has a WORD-sized (two bytes) variable, called Duty. He's then assigning the high byte of Duty to PDC0H ( PDC0H=Duty.HighByte ) and the low byte of Duty to PDC0L ( PDC0L = Duty.LowByte ).

I'll have to read the datasheet for the deadtime thing and I don't have time for that at the moment, I'll try to get back to it later.

/Henrik.

[HenrikOlsson]

Hello again,
If Fosc=10MHz then Tosc=100ns. If you select the source for the Dead Time unit to be Fosc/2 then one "unit" of dead time equals 200ns. You want 5us deadtime which equals 25 "units" of 200ns each so the lower 6 bits of DTCON should be set to 25. If you're using the Fosc/4 setting then one "unit" of deadtime is 400ns and the lower 6 bits would have to be to set to 12.5 to get exactly 5us which obviously isn't possible - use 12 or 13.

/Henrik.

[Kloney]

Hello again,
If Fosc=10MHz then Tosc=100ns. If you select the source for the Dead Time unit to be Fosc/2 then one "unit" of dead time equals 200ns. You want 5us deadtime which equals 25 "units" of 200ns each so the lower 6 bits of DTCON should be set to 25. If you're using the Fosc/4 setting then one "unit" of deadtime is 400ns and the lower 6 bits would have to be to set to 12.5 to get exactly 5us which obviously isn't possible - use 12 or 13.

/Henrik.

Oh .. I didn't notice this comment when did it show up ? thanks Henrick
but still the only left problem is the delay thing which is leading to a lower output frequency.
Also I made an array to lookup up entries and I'm not sure i I'm doing it the right way..
I had to declare each entry in the array one by one .. also compiler refuse using .Lowbyte and .Highbyte (ex : pdc0l=duty[i].lowbyte) with arrays so I made two arrays one for pdcxL and another for pdcxH
is there any other way to declare an array ? or other other function for this case ?

[HenrikOlsson]

Hi,
Without seeing your actual code it's hard to tell what you're doing and if it's "the right way" or not. If it works then I guess it's OK.
But anyway, here are couple of random thoughts....
You don't need an array (in RAM) since the values are constants, use a lookup table (which stores the values in program memory instead of RAM). If the values you're looking up are WORDs you need to use LOOKUP2.

i VAR BYTE
DUTY VAR WORD
MAIN:
  For i = 0 to 8
    LOOKUP2 [100,123,234,345,456,789,890,1234,2345], Duty
    PDC0L = DUTY.LOWBYTE
    PDC0H = DUTY.HIGHBYTE
    PAUSEUS 800
  NEXT
GOTO Main

As for the delay, again hard to tell what you're doing and I'm not sure I understand what the actual problem is. If you want higher output frequency (ie the sine output, not the actual PWM frequency) then reduce the delay between each update of the dutycycle. If the math doesn't add up, make SURE the PIC is running at the frequency you think it is.

/Henrik.

[Kloney]

Hi,
seems I should use Interrupt somehow which I don't have any idea about using it in such a thing..
anyway here's the code

DEFINE OSC 40
 portb = 0
 latb = 0
 TRISB = %11000000 ' pwm0-5 output
 PTCON0 = %00000000 '   (1:1) prescale , Free-running mode 
 PTCON1 = %10000000 'time base is on, Counting is up
PWMCON0 = %01000000 'Pwm0-5 enbbled for pwm output,Complementary
PWMCON1 = %00000001 
OVDCOND = %11111111
DTCON = %01110010 '5us dead-time
PTPERL = $E7
PTPERH = $03
i var byte
x var byte
z var byte
i=0
x=33
z=66
duty var byte[101]
duty2 var byte[101]
duty[0]=05
duty2[0]=00 
duty[1]=05
duty2[1]=31 
duty[2]=05
duty2[2]=63
duty[3]=05
duty2[3]=94
duty[4]= 06
duty2[4]=24 
duty[5]=06
duty2[5]=55 
duty[6]=6
duty2[6]=84 
duty[7]=7
duty2[7]=13
duty[8]=7
duty2[8]=41
duty[9]=7
duty2[9]=68
duty[10]=7
duty2[10]=94
duty[11]=8
duty2[11]=91 
duty[12]=8
duty2[12]=42 
duty[13]=8
duty2[13]=64
duty[14]=8
duty2[14]=85
duty[15]=09
duty2[15]=05
duty[16]=9
duty2[16]=22
duty[17]=9
duty2[17]=38
duty[18]=9
duty2[18]=52 
duty[19]=9
duty2[19]=65 
duty[20]=9
duty2[20]=76 
duty[21]=9
duty2[21]=84 
duty[22]=9
duty2[22]=91 
duty[23]=9
duty2[23]=96 
duty[24]=9
duty2[24]=99 
duty[25]=10
duty2[25]=00 
duty[26]=9
duty2[26]=99 
duty[27]=9
duty2[27]=96 
duty[28]=9
duty2[28]=91 
duty[29]=9
duty2[29]=84 
duty[30]=9
duty2[30]=76 
duty[31]=9
duty2[31]=65 
duty[32]=9
duty2[32]=52 
duty[33]=9
duty2[33]=38 
duty[34]=9
duty2[34]=22 
duty[35]=9
duty2[35]=05 
duty[36]=8
duty2[36]=85 
duty[37]=8
duty2[37]=64 
duty[38]=8
duty2[38]=42 
duty[39]=8
duty2[39]=91 
duty[40]=7
duty2[40]=94 
duty[41]=7
duty2[41]=68 
duty[42]=7
duty2[42]=41 
duty[43]=7
duty2[43]=31 
duty[44]=6
duty2[44]=84 
duty[45]=6
duty2[45]=55 
duty[46]=6
duty2[46]=42 
duty[47]=5
duty2[47]=49 
duty[48]=5
duty2[48]=63 
duty[49]=5
duty2[49]=31 
duty[50]=05
duty2[50]=00 
duty[51]=4
duty2[51]=69 
duty[52]=4
duty2[52]=37  
duty[53]=4
duty2[53]=06 
duty[54]=3
duty2[54]=76 
duty[55]=3
duty2[55]=45 
duty[56]=3
duty2[56]=16 
duty[57]=2
duty2[57]=87 
duty[58]=2
duty2[58]=59 
duty[59]=2
duty2[59]=32 
duty[60]=2
duty2[60]=06 
duty[61]=1
duty2[61]=81 
duty[62]=1
duty2[62]=58
duty[63]=1
duty2[63]=36 
duty[64]=1
duty2[64]=15 
duty[65]=0
duty2[65]=59 
duty[66]=0
duty2[66]=78 
duty[67]=0
duty2[67]=62 
duty[68]=0
duty2[68]=48 
duty[69]=0
duty2[69]=35 
duty[70]=0
duty2[70]=24 
duty[71]=0
duty2[71]=16 
duty[72]=0
duty2[72]=09 
duty[73]=0
duty2[73]=04 
duty[74]=0
duty2[74]=01 
duty[75]=0
duty2[75]=0 
duty[76]=00
duty2[76]=01 
duty[77]=0
duty2[77]=04 
duty[78]=0
duty2[78]=09 
duty[79]=0
duty2[79]=16 
duty[80]=0
duty2[80]=24 
duty[81]=0
duty2[81]=35 
duty[82]=0
duty2[82]=48 
duty[83]=0
duty2[83]=62  
duty[84]=0
duty2[84]=78 
duty[85]=0
duty2[85]=95 
duty[86]=01
duty2[86]=15 
duty[87]=01
duty2[87]=36
duty[88]=01
duty2[88]=58 
duty[89]=01
duty2[89]=81 
duty[90]=02
duty2[90]=06 
duty[91]=02
duty2[91]=32 
duty[92]=02
duty2[92]=59 
duty[93]=02
duty2[93]=87 
duty[94]=03
duty2[94]=16 
duty[95]=03
duty2[95]=45 
duty[96]=03
duty2[96]=76 
duty[97]=04
duty2[97]=06 
duty[98]=04
duty2[98]=37 
duty[99]=04
duty2[99]=96 

Main:

pdc0l=duty2[i]
pdc0h=duty[i]

pdc1l=duty2[x]
pdc1l=duty[x]

pdc2l=duty2[z]
pdc2h=duty[z]
pauseus 100
i=i+1
x=x+1
z=z+1
if (x>99) THEN X=0 
IF (I>99) THEN I=0 
IF (Z>99) THEN Z=0
goto main

I'm trying to generate 3 sinwaves with a 120 shift each to use it in a 3-phase inverter ,the output sinewave frequency should be 50Hz.
I think I can use the Lookup2 function to declare the array entries like this :

G VAR BYTE 
Arrayd VAR WORD   
 For G = 0 to 99     
LOOKUP2 [500, 531, 563, 594, 624, 655, 684, 713, 741, 768, 794, 819, 842, 864, 885, 905, 922, 938, 952, 965, 976, 984, 991, 996, 999, 1000, 999, 996, 991, 984, 976, 965, 952, 938, 922, 905, 885, 864, 842, 819, 794, 768, 741, 713, 684, 655, 624, 594, 563, 531, 500, 469, 437, 406, 376, 345, 316, 287, 259, 232, 206, 181, 158, 136, 115, 95, 78, 62, 48, 35, 24, 16, 9, 4, 1, 0, 1, 4, 9, 16, 24, 35, 48, 62, 78, 95, 115, 136, 158, 181, 206, 232, 259, 287, 316, 345, 376, 406, 437, 469], Arrayd     
duty[G] = Arrayd.LOWBYTE     
duty2[G] = Arrayd.HIGHBYTE   
NEXT

not sure if that is going to work

but I think this is not the problem here

[Kloney]

Hi
-Yes it was 1ms not 1us ,and yeah 800us was just fine for dutycycle update you are right.
Tweaking delay, hmmmm .. should I try Higher frequency ?? then (Fpwm= 25 * 50) won't be correct.
that's going to be a problem since I'm going to use 100 entries for a smoother wave.

-Right , I'm going to edit this part

-oops .. I thought he was multiplying, got it now thanks .

-For the DTCON, it's ok I figured it out after re-reading Bruce's example.