sinusoidal PWM

[bwaxing]

i have changed the number of array size together with other modifications but there is no change in the simulation result,it is still a line....

define OSC 20
 
;*****************VARIABLE DECLARATION******************************************
wsave   VAR BYTE    $70     SYSTEM      ' alternate save location for W 
wsave1  VAR BYTE    $A0     SYSTEM      ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM      ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM      ' location for W if in bank3
STEPCOUNT var byte                      'Define stepcount as byte type variable
stepcount = 256
 
;**************SETTING THE REGISTERS WITH APPROPIATE BIT DEFINITION************* 
ADCON0 = %00000000
ADCON1 = %00000000  ;all anolog output
trisb = %11111111   ;define porta as input
trisc = %11111011   ;make ccp1/portc.2 an output pin
trisa = %11111111   ;define porta as input
TMR2 = 16
PR2 = 34           ;set for 36Khz HPWM(=72 steps*10 times*50hz)        
CCP1CON = %000001100       ;set to pwm mode
T2CON=%00000110           ;enable timer2 and set timer2 prescaler value of 1:4
 
;****************A sine lookup table in an array********************************
sineval var byte[73]
sineval[1] = 128      ;0 degree
sineval[2] = 137      ;5 degree
sineval[3] = 146
sineval[4] = 154
sineval[5] = 163
sineval[6] = 171
sineval[7] = 179
sineval[8] = 187
sineval[9] = 194
sineval[10] = 200
sineval[11] = 206
sineval[12] = 212
sineval[13] = 216
sineval[14] = 220
sineval[15] = 224
sineval[16] = 227
sineval[17] = 228
sineval[18] = 229
sineval[19] = 230     ;90 degree
sineval[20] = 229
sineval[21] = 228
sineval[22] = 227
sineval[23] = 224
sineval[24] = 220
sineval[25] = 216
sineval[26] = 212
sineval[27] = 206
sineval[28] = 200
sineval[29] = 194
sineval[30] = 187
sineval[31] = 179
sineval[32] = 171
sineval[33] = 163
sineval[34] = 154
sineval[35] = 146
sineval[36] = 137
sineval[37] = 128  ;180 degree
sineval[38] = 119
sineval[39] = 110
sineval[40] = 102
sineval[41] = 93
sineval[42] = 85
sineval[43] = 77
sineval[44] = 69
sineval[45] = 62
sineval[46] = 56
sineval[47] = 50
sineval[48] = 44
sineval[49] = 40
sineval[50] = 36
sineval[51] = 32
sineval[52] = 29
sineval[53] = 28
sineval[54] = 26
sineval[55] = 26
sineval[56] = 26
sineval[57] = 28
sineval[58] = 29
sineval[59] = 32
sineval[60] = 36
sineval[61] = 40
sineval[62] = 44
sineval[63] = 50
sineval[64] = 56
sineval[65] = 62
sineval[66] = 69
sineval[67] = 77
sineval[68] = 85
sineval[69] = 93
sineval[70] = 102
sineval[71] = 110
sineval[72] =119
 
timerone var word 
 
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System
 
;********Define INT_Handler as ISR********************************************** 
ASM
 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM
 
T1CON = $31    ; Prescaler = 8, TMR1ON          
TMR1L = 255    
TMR1H = 254
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
timerone = $EE16           ;gives about 50 hz sine 
Main:
        pause 5
        'if timerone = $F9FF then timerone = $FF00
 
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------
 
sine:
    TMR1L = timerone.byte0
    TMR1H = timerone.byte1     
    CCPR1L = sineval[STEPCOUNT]>>1 
    stepcount = stepcount -1
    if stepcount = 1 then stepcount = 73
@    INT_RETURN

[cncmachineguy]

First thing I would do is make sure the ISR is working. Make an unused pin an output, then toggle it in the ISR. hook a scope to that and make sure it toggles. Also you can do the same in your main with another pin.

This way you will know some basic info like is my pic running, is my interrupt firing. do that and report back

[bwaxing]

hi,
i've managed to get the sinusoidal output sine wave although i'm getting frequency of 202Hz instead of 50Hz and peak voltage of 4.58v instead of 4.5v.Also the waveform is not smooth.Simulation results.docWhat should i do to acheave this parameters?
code:

define OSC 4
;*****************VARIABLE DECLARATION******************************************
wsave   VAR BYTE    $70     SYSTEM      ' alternate save location for W 
wsave1  VAR BYTE    $A0     SYSTEM      ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM      ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM      ' location for W if in bank3 
ADCON0 = %00000000
ADCON1 = %00000000
trisb = %11111111
trisc = %11111011
trisa = %11111111
TMR2 = 16
PR2 = 15      ;set for 16Khz HPWM        
CCP1CON.3 = 1        ' set to pwm mode
CCP1CON.2 = 1
T2CON.2=1
T2CON.0=1
STEPCOUNT var byte
stepcount = 32
; Set sine "table" in an array
sineval var byte[32]
sineval[1] = 128
sineval[2] = 148
sineval[3] = 167
sineval[4] = 185
sineval[5] = 200
sineval[6] = 213
sineval[7] = 222
sineval[8] = 228
sineval[9] = 230
sineval[10] = 228
sineval[11] = 222
sineval[12] = 213
sineval[13] = 200
sineval[14] = 185
sineval[15] = 167
sineval[16] = 148
sineval[17] = 128
sineval[18] = 108
sineval[19] = 89
sineval[20] = 71
sineval[21] = 56
sineval[22] = 43
sineval[23] = 34
sineval[24] = 28
sineval[25] = 26
sineval[26] = 28
sineval[27] = 34
sineval[28] = 43
sineval[29] = 56
sineval[30] = 71
sineval[31] = 89
sineval[32] = 108
 
 
timerone var word 
 
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System
;include "ReEnterPBP-18.bas"  ;not needed for ASM type interrupt service routines
 
ASM
 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM
 
T1CON = $31                 ; Prescaler = 8, TMR1ON
TMR1L = 255
TMR1H = 254
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
timerone = 65504               ;gives about 50 htz sine 
Main:
        pause 5
        'timerone = timerone - 1      'uncomment to vary 60hz sine
        if timerone = $F9FF then timerone = $FF00
 
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------
 
sine:
    TMR1L = timerone.byte0
    TMR1H = timerone.byte1     
    CCPR1L = sineval[STEPCOUNT]>>1 
    stepcount = stepcount -1
    if stepcount = 0 then stepcount = 32
 
@    INT_RETURN

[HenrikOlsson]

Hi,
You're still off on the array.

Sinval VAR BYTE[32]

This creates an array of 32 elements numbered 0-31 but you assign values to it starting at 1 and ending at 32 - not very good. There is no SineVal[32], when you read/write to that variable you're actually accessing the "next" RAM location, something I'm sure you don't want to do here.

You can adjust the peak value by "scaling" the value in your sine-table but really, you're not even 2% off target.

Are you using a 4MHz x-tal like the code says or are you using something else?

If I'm not mistaken a reload value of 65505 with a prescaler of 1:8 running at 4Mhz gives an interrupt frequency of 4032Hz, you have 32 "steps" to your cycle so you "should" get around 126Hz....

For accuracy it's usually better to stop the timer and then ADD the preload value to the timers current value since this will take into account the interrupt latency etc. Stop it, copy it to a WORD, add the reload value, copy it back and restart the timer.

Any specific reason you're using a TMR1 prescaler of 8? Using a lower prescaler ratio will give you better "resolution" on the interrupt frequency.

/Henrik.

[bwaxing]

hellow Henrik,
thanx for the tips, i've re-worked my sine table,also i've include the code for accuracy although i'm not sure if i've place it in a right place!
For a 4MHz xtal and TMR1 prescaler of 1 i reload the T1 with the value 64980 to get 50Hz and it's what m getting on the scope.
Also TMR2 with prescaler of 4 is loaded with 117 for the interrupt to be generated every 556us(256-(556/(4*0.25*4))
But the problem is that the waveform i'm getting on the scope is not smooth at all....Simulation results..pdf

code:

define OSC 4
 
;*****************VARIABLE DECLARATION******************************************
wsave   VAR BYTE    $70     SYSTEM      ' alternate save location for W 
wsave1  VAR BYTE    $A0     SYSTEM      ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM      ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM      ' location for W if in bank3
STEPCOUNT var byte                      'Define stepcount as byte type variable
stepcount = 36
 
;**************SETTING THE REGISTERS WITH APPROPIATE BIT DEFINITION************* 
ADCON0 = %00000000
ADCON1 = %00000000  ;all anolog output
trisb = %11111111   ;define porta as input
trisc = %11111011   ;make ccp1/portc.2 an output pin
trisa = %11111111   ;define porta as input
TMR2 = 117
PR2 = 13          ;set for 18Khz HPWM(=36 steps*10 times*50hz)        
CCP1CON = %000001100       ;set to pwm mode
T2CON=%00000110           ;enable timer2 and set timer2 prescaler value of 1:4
 
;****************A sine lookup table in an array********************************
sineval var byte[36]
sineval[0] = 128
sineval[1] = 148
sineval[2] = 167
sineval[3] = 185
sineval[4] = 201
sineval[5] = 215
sineval[6] = 227
sineval[7] = 235
sineval[8] = 240
sineval[9] = 242
sineval[10] = 240
sineval[11] = 235
sineval[12] = 227
sineval[13] = 215
sineval[14] = 201
sineval[15] = 185
sineval[16] = 167
sineval[17] = 148
sineval[18] = 128
sineval[19] = 108
sineval[20] = 89
sineval[21] = 71
sineval[22] = 55
sineval[23] = 41
sineval[24] = 29
sineval[25] = 21
sineval[26] = 16
sineval[27] = 14
sineval[28] = 16
sineval[29] = 21
sineval[30] = 29
sineval[31] = 41
sineval[32] = 55
sineval[33] = 71
sineval[34] = 89
sineval[35] = 108
 
timerone var word 
 
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System
 
;********Define INT_Handler as ISR********************************************** 
ASM
 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM
 
T1CON = %000001    ; Prescaler = 1, TMR1ON          
TMR1L = 255    
TMR1H = 254
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
timerone = 64980           ;gives about 50 hz sine 
Main:
        pause 5
 
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------
 
'accuracy thing
TimerShadow VAR WORD
T1CON.0 = 0  'Stop TMR1
TimerShadow.HighByte = TMR1H
TimerShadow.LowByte = TMR1L
TimerShadow = TimerShadow + Timerone
TMR1H = TimerShadow.HighByte
TMR1L = TimerShadow.LowByte
T1CON.0 = 1  'Restart TMR1
sine:
    TMR1L = timerone.byte0
    TMR1H = timerone.byte1     
    CCPR1L = sineval[STEPCOUNT]>>1 
    stepcount = stepcount -1
    if stepcount = 0 then stepcount = 36
@    INT_RETURN

where i'm wrong in the code? are the calculations above correct?

[ScaleRobotics]

What are you using for a filter? You should have at least half of the below example to smooth out the signal. Also, it will never look too good on simulation. Might look better on actual hardware. Might be some issues with running it at 4 mhz. Is there a reason you don't want 20 mhz? Even AN655 's example showed 20 mhz.

;   Filter Diagram
;        
;               2.7k            2.7k    
;    RC2  ___/\  /\  /\______/\  /\  /\________ Analog Output
;              \/  \/    |     \/  \/     |  
;                        |                |
;                      ----- 0.1uF      ----- 0.1uF
;                      -----            -----
;                        |                |
;                       GND              GND
;
;

[bwaxing]

the 877 pic on the board i'm using have 4Mhz clock, and i'm using the same filter as above.are the calculations above correct?

[HenrikOlsson]

Hi,
Several things.....
TMR2 is the timer used for the PWM generation. The fact that you initially load it with 117 doesn't matter for either the PWM frequency or your interrupt frequency since you're using TMR1 to generate the interrupts.

You have the prescaler for TMR2 set to 1:4 and PR2 set to 13 which indeed gives you ~18kHz PWM frequency but it'll only give you a give you 56 discrete dutycycles. Ie. the maximum value you can put in the dutycycle register is 56. The highest value in your sine table is 242 which you then shift right one time bofore putting in the CCP1L, so you're trying to put 121 in there when 56 is max.

Changing the prescaler to 1:1 and putting 55 in PR2 gives you the same PWM frequency but allows dutycycle values of 0-222.

TMR1 is now setup with a prescaler of 1:1 and you reload it with 64980 making it interrupt every 65536-64980=556us or at a frequency of 1798Hz, there's now 36 steps to your "cycle" so 1798/36=49.96Hz so it seems to be correct. I don't think you should expect to be able to run much faster than that at 4Mhz, the DT-ints takes quite afew cycles to save and restore all the system variables on each interrupt so you won't have much time left.

The "accuracy thing" needs to be performed on each reload or it won't have much effect. It should be in your ISR instead of the reload code you have there now.

/Henrik.

[ScaleRobotics]

Hi Henrik! As always, great post!
I've done some work with DT_INTS, and in ASM mode, they are fairly fast, as they only copy a few registers, vs the PBP type, which copies then restores about 70 registers with each interrupt. So I don't understand your warning about going above 4 Mhz? I've run it at 40 Mhz on a different chip and it worked pretty well using ASM type DT_INTS.

[bwaxing]

Hi,
Several things.....
TMR2 is the timer used for the PWM generation. The fact that you initially load it with 117 doesn't matter for either the PWM frequency or your interrupt frequency since you're using TMR1 to generate the interrupts.

You have the prescaler for TMR2 set to 1:4 and PR2 set to 13 which indeed gives you ~18kHz PWM frequency but it'll only give you a give you 56 discrete dutycycles. Ie. the maximum value you can put in the dutycycle register is 56. The highest value in your sine table is 242 which you then shift right one time bofore putting in the CCP1L, so you're trying to put 121 in there when 56 is max.

Changing the prescaler to 1:1 and putting 55 in PR2 gives you the same PWM frequency but allows dutycycle values of 0-222.

TMR1 is now setup with a prescaler of 1:1 and you reload it with 64980 making it interrupt every 65536-64980=556us or at a frequency of 1798Hz, there's now 36 steps to your "cycle" so 1798/36=49.96Hz so it seems to be correct. I don't think you should expect to be able to run much faster than that at 4Mhz, the DT-ints takes quite afew cycles to save and restore all the system variables on each interrupt so you won't have much time left.

The "accuracy thing" needs to be performed on each reload or it won't have much effect. It should be in your ISR instead of the reload code you have there now.

/Henrik.

i've the changes in the code as you suggested above,but the waveform is still not smooth....Simulation results..pdf

define OSC 4

;*****************VARIABLE DECLARATION******************************************
wsave   VAR BYTE    $70     SYSTEM      ' alternate save location for W 
wsave1  VAR BYTE    $A0     SYSTEM      ' location for W if in bank1
wsave2  VAR BYTE    $120    SYSTEM      ' location for W if in bank2
wsave3  VAR BYTE    $1A0    SYSTEM      ' location for W if in bank3
STEPCOUNT var byte                      'Define stepcount as byte type variable
stepcount = 36

;**************SETTING THE REGISTERS WITH APPROPIATE BIT DEFINITION************* 
ADCON0 = %00000000
ADCON1 = %00000000  ;all anolog output
trisb = %11111111   ;define porta as input
trisc = %11111011   ;make ccp1/portc.2 an output pin
trisa = %11111111   ;define porta as input
TMR2 = 117
PR2 = 55          ;set for 18Khz HPWM(=36 steps*10 times*50hz)        
CCP1CON = %000001100       ;set to pwm mode
T2CON=%00000100           ;enable timer2 and set timer2 prescaler value of 1:1

;****************A sine lookup table in an array********************************
sineval var byte[36]
sineval[0] = 128
sineval[1] = 148
sineval[2] = 167
sineval[3] = 185
sineval[4] = 201
sineval[5] = 215
sineval[6] = 227
sineval[7] = 235
sineval[8] = 240
sineval[9] = 242
sineval[10] = 240
sineval[11] = 235
sineval[12] = 227
sineval[13] = 215
sineval[14] = 201
sineval[15] = 185
sineval[16] = 167
sineval[17] = 148
sineval[18] = 128
sineval[19] = 108
sineval[20] = 89
sineval[21] = 71
sineval[22] = 55
sineval[23] = 41
sineval[24] = 29
sineval[25] = 21
sineval[26] = 16
sineval[27] = 14
sineval[28] = 16
sineval[29] = 21
sineval[30] = 29
sineval[31] = 41
sineval[32] = 55
sineval[33] = 71
sineval[34] = 89
sineval[35] = 108
 
timerone var word 
TimerShadow VAR WORD 
INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System

;********Define INT_Handler as ISR********************************************** 
ASM 
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   _sine,   ASM,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

T1CON = %000001    ; Prescaler = 1, TMR1ON          
TMR1L = 255    
TMR1H = 254
@   INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
timerone = 64980           ;gives about 50 hz sine 
Main:
        pause 5
        
GOTO Main
 
'---[TMR1_INT - interrupt handler]------------------------------------------


sine:
'accuracy thing
T1CON.0 = 0  'Stop TMR1
TimerShadow.HighByte = TMR1H
TimerShadow.LowByte = TMR1L
TimerShadow = TimerShadow + Timerone
TMR1H = TimerShadow.HighByte
TMR1L = TimerShadow.LowByte
T1CON.0 = 1  'Restart TMR1

    TMR1L = timerone.byte0
    TMR1H = timerone.byte1     
    CCPR1L = sineval[STEPCOUNT]>>1 
    stepcount = stepcount -1
    if stepcount = 0 then stepcount = 36

@    INT_RETURN

[Russ Kincaid]

Check into Don Lancaster's Magic Sinewaves here: http://www.tinaja.com/
I did it with a basic stamp BS1 several years ago when I was a newby, it is quite simple and works great.

[sangaboy]

Hi!

I manage to compile and modify the example from that link www.picbasic.co.uk/forum/cont...-DT-interrupts, for pic 16877. Because the pic I want to use for three phase spwm signal is (16f777) which has 3 CCP module and I' m waiting for it to come the problem it is not includeded in ISIS simulator that is why I used pic 168777 having 2 CCP module for simulation and is present in ISIS and my college lab. I belive if I manage to generate two phase spwm it became eaasy for 3 phase spmw.

here is the code and attachement of my output from ISIS and mysinelooktable and
define OSC 4

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

TRISB = %11111111
TRISC = %11111001 'PMW output for CCP1 AND CCP2
TRISA = %11111111
TMR2 = 117
PR2 = 55 '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 byte[36]
sineval[0] = 128
sineval[1] = 150
sineval[2] = 171
sineval[3] = 191
sineval[4] = 209
sineval[5] = 225
sineval[6] = 238
sineval[7] = 247
sineval[8] = 253
sineval[9] = 255
sineval[10] = 253
sineval[11] = 247
sineval[12] = 238
sineval[13] = 225
sineval[14] = 209
sineval[15] = 191
sineval[16] = 171
sineval[17] = 150
sineval[18] = 128
sineval[19] = 105
sineval[20] = 84
sineval[21] = 64
sineval[22] = 46
sineval[23] = 30
sineval[24] = 17
sineval[25] = 8
sineval[26] = 2
sineval[27] = 0
sineval[28] = 2
sineval[29] = 8
sineval[30] = 17
sineval[31] = 30
sineval[32] = 46
sineval[33] = 64
sineval[34] = 84
sineval[35] = 105

timerone var word
Temp var byte
Temp1 var byte

INCLUDE "DT_INTS-14.bas" ; Base Interrupt System emp


ASM

INT_LIST macro ; IntSource, Label, Type, ResetFlag?
INT_Handler TMR1_INT, _sine, ASM, yes
endm
INT_CREATE ; Creates the interrupt processor
ENDASM

T1CON = 000001 ; Prescaler = 1;1, TMR1 ON
TMR1L = 255
TMR1H = 254
@ INT_ENABLE TMR1_INT ; Enable Timer 1 Interrupts

timerone = 64980 ;gives about 50 htz sine
Main:
PAUSE 5

GOTO Main

'---[TMR1_INT - interrupt handler]------------------------------------------

sine:
TMR1L = timerone.byte0
TMR1H = timerone.byte1

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 = Temp.0 ' bit 0
CCP2CON.5 = Temp.1 ' bit 1
CCPR2L = Temp >>2 'Bit 2-7
if stepcount = 36 then stepcount =0
if stepcount1 = 24 then stepcount1 =0
stepcount = stepcount +1
stepcount = stepcount1 +1

@ INT_RETURN



any one can help me