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PWM in 16F873A

 
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zonared



Joined: 24 Mar 2004
Posts: 4

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PWM in 16F873A
PostPosted: Tue Nov 16, 2004 4:26 am     Reply with quote
I have been trying to setup a simple PWM for awhile now with this chip. It produces some bazaar results. Code is as follows:

set_tris_a(0b11101111);
set_tris_b(0b00000000);
set_tris_c(0b11011000);

setup_port_a(AN0);
setup_adc(adc_clock_internal);
set_adc_channel( 0 );

setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_16, 127, 4); // 10Mhz crystal

main()
{
ADInValue = read_adc();
printf("ADInValue=%03u%c",ADInValue,13);
set_pwm1_duty(ADInValue);
}

With this code the PWM output turns motor full on until count gets above ~250 and motor slows a little... What should I look for to fix this, code looks like the example file EX_PWM.C

Confused Confused ,
Zonared.
Ttelmah
Guest
Re: PWM in 16F873A
PostPosted: Tue Nov 16, 2004 4:47 am     Reply with quote
zonared wrote:
I have been trying to setup a simple PWM for awhile now with this chip. It produces some bazaar results. Code is as follows:

set_tris_a(0b11101111);
set_tris_b(0b00000000);set_tris_c(0b11011000);

setup_port_a(AN0);
setup_adc(adc_clock_internal);
set_adc_channel( 0 );

setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_16, 127, 4); // 10Mhz crystal

main()
{
ADInValue = read_adc();
printf("ADInValue=%03u%c",ADInValue,13);
set_pwm1_duty(ADInValue);
}

With this code the PWM output turns motor full on until count gets above ~250 and motor slows a little... What should I look for to fix this, code looks like the example file EX_PWM.C

Confused Confused ,
Zonared.


Try executing the setup instructions!.....
All the 'setup' commands, need to actually be run. You have placed them outside the main, and they will never be called. Either use:
Code:

void init_ports(void) {
   set_tris_a(0b11101111);
   set_tris_b(0b00000000);
   set_tris_c(0b11011000);
     
   setup_port_a(AN0);
   setup_adc(adc_clock_internal);
   set_adc_channel( 0 );

   setup_ccp1(CCP_PWM);
   setup_timer_2(T2_DIV_BY_16, 127, 4);   // 10Mhz crystal
}

main()
{
   init_ports();
   ADInValue = read_adc();
   printf("ADInValue=%03u%c",ADInValue,13);
   set_pwm1_duty(ADInValue);
}

Or put the instructions inside your main.

You need to understand, that C will accept a declaration like this, assuming it to be a 'function prototype', and giving no errors, but the code is never run, unless it is put into the the actual body of the program somewhere...
Note also, using the 'Code' button, makes code put into postings, much easier to read.

Best Wishes
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