Seeking HELP for PIC12F683 PWM output

[djpark]

I thought this is going to be a simple practice, but turned out to be a mistery to me. Can someone point out what is wrong and advice to correct to get the PWM output using PIC12F683? I am using PIN_A2 (CCP1) as led output.

TIA,

-- dj

[PCM programmer]

One problem I can see immediately is that you're trying to set
the PWM duty cycle to be longer than the period.

The 12F683, in section 11.3.2, says:
"Note: If the PWM duty cycle value is longer than
the PWM period, the CCP1 pin will not be cleared".

This means the output stays at a high level.

You've set the PWM period to 0x3F here:
setup_timer_2(T2_DIV_BY_1, 0x3f, 1);

But then here, you're setting the PWM duty cycle
to a value greater than 0x3F.
for (duty=1; duty<255; duty++)
{
set_pwm1_duty(duty);


See this post for more info:
http://www.ccsinfo.com/forum/viewtopic.php?t=17729

[djpark]

Thanks for the info. But I think I am missing something very basic.

When I tried the following code, it doesn't turn on the led connected to PIN_A2 at all.

Is there anything else I need to setup to use the PWM?

-- dj

[PCM programmer]

In the link that I posted, there is sample code at the end of the thread.

Look at the last line in that sample program.

Look at the comment on that last line.

[djpark]

Sorry, it was my mistake to omit from the source posted. But it is actually there in my test program as below.

[PCM programmer]

Post your version of the compiler.

I'll compile the program with that version and look at the ASM code.

[djpark]

Thanks for help.

I use PCM 3.187 and it generated the following LST.

[DragonPIC]

Did you check your hardware?
_________________
-Matt

[PCM programmer]

Your version of the compiler is buggy with the 12F683.
You will need to make the changes shown in bold below.

Reasons:

Problems with the start-up code:
The compiler is calling address 0x7FF, as if this PIC has an OSCCAL
value at that address. However, it does not, so this is a bug.
Also, the value is being put into the OSCTUNE register, since this
PIC has no OSCCAL register.
The work-around is to use a #rom statement to place a RETLW 0
opcode there. This will cause your version of the compiler to load 0
into the OSCTUNE register, which is the power-up default value.
Doing this will fix the bug.

Problems with setup_ccp1(CCP_PWM):
The compiler is setting up the wrong port and the wrong pin for
the PWM output. By doing output_low(PIN_A2) in standard i/o mode,
we can fix this. The compiler is also using the wrong address for
the CCP1CON register. We can fix this by defining the register address
with a #byte statement, and then writing to it directly with a line of code.

Problems with set_pwm1_duty(100):
The compiler is using the wrong address for the CCPR1L register.
We can fix this by defining the CCPR1L address with a #byte statement
and writing directly to the register with a line of code.

My comment: Your version of the compiler is buggy with this PIC.
Assume that there may be other bugs that you may discover in the
future.

#include <12F683.h>
#fuses NOWDT, INTRC_IO, NOCPD, NOPROTECT, NOMCLR, NOPUT,
NOBROWNOUT, NOIESO, NOFCMEN
#use delay (clock=8000000)

#ROM 0x7FF = {0x3400} // Add this line
#byte CCPR1L = 0x13
#byte CCP1CON = 0x15

void main()
{
setup_oscillator(OSC_8MHZ);

setup_adc_ports(NO_ANALOGS);
setup_adc(ADC_OFF);
setup_comparator(NC_NC);
setup_vref(FALSE);

set_tris_a(0b11111011);

setup_timer_2(T2_DIV_BY_1, 124, 1);

// setup_ccp1(CCP_PWM); // Comment out this line

output_low(PIN_A2); // Add this line
CCP1CON = CCP_PWM; // Add this line


// set_pwm1_duty(100); // Comment out this line
CCPR1L = 100; // Add this line

while(1);

}

[djpark]