Redefining HPWM as output

Hello Everyone. I have a 16F818 and am using it's PWM on Rb2 to generate tones, coupling it through a FET (N channel). The drain on the FET goes to a speaker terminal. The other speaker terminal goes to B+. It works perfectly except, a couple of seconds after playing the tone, Rb2 goes HIGH causing the FET to turn on and the speaker consumes a lot of power. If you look at the START of my program you will see that I attempted to convert Rb2 as output low. It does NOT. I only included NOTE1 to shorten this post. Any suggestions? Thank you.

OSCCON = $60 '4mhz 'set int osc to 4mhz
adcon1 = 7 ' set inputs to digital
DEFINE CCP1_BIT 2 'PWM OUTPUT ON Rb2
TRISA = %11111111 'INPUT SWITCHES
TRISB = 0 'PORTB OUTPUT
PORTB = 0 'ALL LOW
@ DEVICE MCLR_OFF, INTRC_OSC, WDT_ON, LVP_OFF, BOD_OFF, PWRT_ON, PROTECT_ON
Pause 500

START:
PORTB = 0 'ALL LEDS OFF
Output PORTB.2 'ATTEMPT TO REDEFINE RB2 AS OUTPUT LOW DOESN'T WORK
Low PORTB.2
NAP 2
IF PORTA.1 = 1 Then NOTE1
IF PORTA.0 = 1 Then NOTE2
IF PORTA.7 = 1 Then NOTE3
IF PORTA.6 = 1 Then NOTE4
IF PORTA.2 = 1 Then NOTE5
IF PORTA.3 = 1 Then NOTE6
IF PORTA.4 = 1 Then NOTE7
GoTo START

NOTE1:
HPwm 1,127,522 "PLAY SOUND
High PORTB.7 "ON LED
IF PORTA.1 = 1 Then NOTE1 'IF SWITCH ON KEEP PLAYING
HPwm 1,127,0 'TURN OFF SOUND
GoTo START

what about if you place a LOW PORTB.2 after the last HPWM line???

EDIT: i think i need to sleep.. See Alain solution...

Hi, Peterdeco

Melabs says : to stop HPWM : HPWM 1, 0, xxxx ( duty cycle to zero ! )

That's all !!!

Now, if you can decently explain what PBP does when you ask for 0 Hz freq ...

you could also disable the CCP1 module ... but why ???

Alain

Hi,

Do you have to change the frequency to zero?
I wouldn't.
Anything below the minimum allowed frequency can cause strange results with the HPWM command.
I think if you simply issue the command at the frequency you've been using, but at a 0% duty cycle, it will be solid OFF. If you issue the command with a 100% duty cycle (255 if 8-bit) it will be solid ON.

Does anybody see any problem with this approach?

Regards,

Quote:

---

Originally Posted by Picnaut

Does anybody see any problem with this approach?

---

Can't say... i never use HPWM. Still prefer to write directly to the internal register. BUT, as Alain said and AS per the book

Quote:

---

Originally Posted by TFM

Dutycycle specifies the on/off (high/low) ratio of the signal. It ranges from 0 to 255, where 0 is off (low all the time) and 255 is on (high) all the time.

---

If you want to turn OFF hardware PWM & have a solid logic output on the CCP pin, don't rely on using the HPWM command with a zero duty-cycle. Just use CCP1CON = 0 to disable the PWM module, then set/clear the pin as required.

After clearing CCP1CON, you can simply issue the HPWM command again, and PBP will automatically configure CCP1CON for PWM mode.

Some I/O-pins are multiplexed with peripherals. When these peripherals are enabled, they may "override" the TRIS bit for a pin. Even though the HPWM command does leave the TRIS bit set to output, and it leaves a zero in the output latch, if the PWM module is still enabled, and not outputting a PWM signal, you'll see a high impedance on the CCP output pin.

Quote:

---

Originally Posted by picnaut

Hi,

I think if you simply issue the command at the frequency you've been using, but at a 0% duty cycle, it will be solid OFF. If you issue the command with a 100% duty cycle (255 if 8-bit) it will be solid ON.

Does anybody see any problem with this approach?

Regards,

---

Hi, Picnaut

this approach runs perfectly well, and it is recommended by Melabs itself ...as I use HPWM for R/C E-motors , I just clear CCP1CON when I'm not really really sure a glitch could give a false value to duty cycle. ( never saw it ...but i'm sure !!! )

Alain

Thank you Everybody. Bruce, I did the CCP1CON = 0 thing in place of my "zero frequency" command and it works like a charm.

Bruce's approach sounds better to me.
It probably uses less code than issuing the HPWM command again also.

Cheers.

Here's a simple test to show the effects of disabling the hardware PWM module, or using a zero duty-cycle or freq with HPWM.

Hook an LED up to your CCP out pin.

CCP output pin ---|>|----/\/\/\/\----GND

Code:

---

SYMBOL PIN = PORTC.2 ' Define whatever pin on your PIC is CCP out here

    HPWM 1,127,2000
    PAUSE 8000
    CCP1CON = 0 ' Test once with this, then comment it out
    'HPWM 1,0,0  ' Now test with this un-commented
   
WAITUP:
    HIGH PIN
    PAUSE 500
    LOW PIN
    PAUSE 500
    GOTO WAITUP

---

On a 16F876A, the LED never toggles with HPWM 1,0,0. It does once the hardware PWM module is disabled with CCP1CON = 0. I'm curious if it works either way on other PIC's.

Hi Bruce,

Try it again, but this time leave the frequency at 2000 (only the duty cycle is 0). See if it toggles then.
I'm curious (and no where near a PIC right now).

Cheers!

Hi Bruce,

Also, maybe put a 500ms delay right after the "WAITUP" label. Otherwise, if PIN goes low, it will immediately go high again and you won't catch it.


Cheers!

Works the same until CCP1CON = 0.

Another delay isn't really necessary since it never toggles the LED to begin with.

I find that setting duty to 0 allows the pin to float
and that can cause a fet to turn on.
I add a weak pull down resistor to the pin used
or set the output to low when duty=0