Modifying Darrel's SSPWM resolution?

[retepsnikrep]

I tinkered around and found that with my 8mhz int clock and 2khz pwm the prescaler was being set to 1 and ticks was 1000 per cycle. 50% duty Time on/off was 500 ticks each. This suggests that resolution can be increased to 0.1% by changing DutyCycle to a word variable and using 500 instead of 50 to represent 50% duty. I have adjsted the calculation so it now ranges from 0-1000 in steps of 1 instead of steps of 10. I also removed all the calculation routines as ticks are now known as is prescaler etc. That save quite a few bytes as well

Darrel any comments?

Peter

[Darrel Taylor]

Sounds like you have it under control Peter.

The numbers look good to me.

[Tobias]

Is it possible to keep duty cycle a constant and vary the frequency?

[Darrel Taylor]

That wouldn't be PWM.
It would be a variable frequency generator.

Much easier to do, but you don't need SSPWM.

[retepsnikrep]

Just as a final follow up I hacked SSPWM down to a fraction of it's original size and it works great.

I use the 8mhz internal osc and for my reqd 2000hz freq that works out at a very simple 1000 ticks per cycle

DEFINE INTHAND INT_CODE ' Tell PBP Where the code starts on an interrupt

wsave VAR BYTE $20 SYSTEM '$20 Save location for the W register if in bank0
wsave1 VAR BYTE $A0 SYSTEM ' Save location for the W register if in bank1
wsave2 VAR BYTE $120 SYSTEM ' Save location for the W register if in bank2
wsave3 VAR BYTE $1A0 SYSTEM ' Save location for the W register if in bank3
ssave VAR BYTE Bank0 SYSTEM ' Save location for the STATUS register
psave VAR BYTE Bank0 SYSTEM ' Save location for the PCLATH register

TMR1_ON_TICKS var word Bank0 ' # of Tmr ticks for On Time
TMR1_OFF_TICKS var word Bank0 ' # of Tmr ticks for Off Time
TMR1_ON_VAL var word Bank0 ' # to load TMR1 for On Time
TMR1_OFF_VAL var word Bank0 ' # to load TMR1 for Off Time

DataFlags var byte Bank0
SPWMstate var DataFlags.2 ' Current state of SPWM output high or low

GIE var INTCON.7
PEIE var INTCON.6
TMR1IE var PIE1.0
TMR1ON var T1CON.0

clear 'Clear All Variables

goto Start

' ------------------------------------------------------------------------
asm
INT_CODE
if (CODE_SIZE <= 2)
movwf wsave ; copy W to wsave register
swapf STATUS,W ; swap status reg to be saved into W
clrf STATUS ; change to bank 0 regardless of current bank
movwf ssave ; save status reg to a bank 0 register
movf PCLATH,w ; move PCLATH reg to be saved into W reg
movwf psave ;6 ; save PCLATH reg to a bank 0 register
endif

btfss PIR1, TMR1IF ; is TMR1IF set? Timer1 Interrupt Flag
GOTO NoTimerInt ; No. Bypass timer load
btfss _SPWMstate ; Is Output High?
GOTO TurnON ;9/15 ; No.

TurnOFF
bcf _CmdPwr ; Set CmdPwr Low
bcf _SPWMstate ;
BCF T1CON,TMR1ON ; Turn off timer
MOVF _TMR1_OFF_VAL,W ; 1
ADDWF TMR1L,F ; 1 ; reload timer with correct value
BTFSC STATUS,C ; 1/2
INCF TMR1H,F ; 1
MOVF _TMR1_OFF_VAL+1,W ; 1
ADDWF TMR1H,F ; 1
BSF T1CON,TMR1ON ; 1 ; Turn it back on
GOTO TimerDone ;12/27

TurnON
bsf _CmdPwr ; Set CmdPwr High
bsf _SPWMstate ;
bcf T1CON,TMR1ON ; Turn off timer
MOVF _TMR1_ON_VAL,W ; 1
ADDWF TMR1L,F ; 1 ; reload timer with correct value
BTFSC STATUS,C ; 1/2
INCF TMR1H,F ; 1
MOVF _TMR1_ON_VAL+1,W ; 1
ADDWF TMR1H,F ; 1
bsf T1CON,TMR1ON ; 1 ; Turn it back on

TimerDone
bcf PIR1, TMR1IF ; 1/28 ; Clear Timer1 Interrupt Flag

NoTimerInt
Movf psave,w ; Restore the PCLATH reg
Movwf PCLATH
swapf ssave,w ; Restore the STATUS reg
movwf STATUS
swapf wsave,f
swapf wsave,w ; 6/34 ; Restore W reg

Retfie ; Exit the interrupt routine

endasm
' ------------------------------------------------------------------------

StartSPWM: 'Set Freq and DutyCycle before calling
'For 2khz pwm and 8mhz clock Ticks = 1000 per cycle
GIE = 1
PEIE = 1
TMR1H = 255 'Load TMR1 with 65535, First tick will cause
TMR1L = 255 'an interrupt that will load TMR1_???_VAL
TMR1_ON_TICKS = DutyCycle '(Must be between 100 & 900 (10-90%)
TMR1_OFF_TICKS = 1000 - TMR1_ON_TICKS
TMR1_ON_VAL = 65535 - TMR1_ON_TICKS + 8
TMR1_OFF_VAL = 65535 - TMR1_OFF_TICKS + 8
TMR1IE = 1
T1CON = 1 'Set Timer1 prescaler to 1 and turn Timer1 on
return

'************************************************* ************************************
'*********************************** Main Program ************************************

I use a word variable for DutyCycle between 0-1000 which gives me a 0.1% resolution now a tenfold increase over the original.
I just load DutyCyle with my reqd duty and call StartSPWM:

Thanks to Darrel for the original code which I now understand as well making some small personal inroads into Pic Assembler

[retepsnikrep]

A couple more questions about this Darrel as i'm trying to understand the code.

In your variable definitions we have

wsave1      VAR BYTE    $A0     SYSTEM          ' Save location for the W register if in bank1
wsave2      VAR BYTE    $120    SYSTEM          ' Save location for the W register if in bank2
wsave3      VAR BYTE    $1A0    SYSTEM          ' Save location for the W register if in bank3

These are not anywhere else in the code? so i don't understand how they are used?
I tried removing them and the program compiled correctly but started giving an eroneous display?

In your Int code you have

asm
INT_CODE
      if (CODE_SIZE <= 2)
        movwf   wsave              ; copy W to wsave register
        swapf   STATUS,W           ; swap status reg to be saved into W
        clrf    STATUS             ; change to bank 0 regardless of current bank
        movwf   ssave              ; save status reg to a bank 0 register
        movf    PCLATH,w           ; move PCLATH reg to be saved into W reg
        movwf   psave       ;6     ; save PCLATH reg to a bank 0 register
       endif

What does " if (CODE_SIZE <= 2)" do?
Clearly it jumps over the register saving stuff but where does CODE_SIZE come from?

2 does that mean 2k or 2 words, bytes?

Thanks Peter

PS I have bought PBP3 looking forward to trying it later

[Darrel Taylor]

This post should cover both of those questions.
http://www.picbasic.co.uk/forum/show...9101#post89101

And yes, 2 means 2K.
It is set in the .bas or .pbpinc files.