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geeth9
Joined: 17 Mar 2010
Posts: 2
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| Generate a 50 Hz signal |
 Posted: Sun Oct 31, 2010 12:20 pm |
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I am trying to generate a PWM sinal with a frequency of 46.5 HZ . I found a post in the forum which explains how to get that. I tried it and the code is:
| Code: |
#include<18f4520.h> //Device Header
#fuses H4,NOPROTECT,NOWDT,PUT // Set Fuses
#use delay(clock=2000000) //20Mhz Clock
#use RS232 (baud=9600, parity = N, xmit = PIN_C6, rcv=PIN_C7)
#define PWM_PIN PIN_E1
#define LOOPCNT 20
int8 width;
//-------------------------------
#INT_RTCC
void tick_interrupt(void);
//====================================
main()
{
width = 15;
setup_counters(RTCC_INTERNAL, RTCC_DIV_1);
enable_interrupts(INT_RTCC);
enable_interrupts(GLOBAL);
while(1);
}
//====================================
#INT_RTCC
void tick_interrupt(void)
{
static int8 loop = LOOPCNT;
static int8 pulse;
if(--loop == 0)
{
loop = LOOPCNT;
pulse = width;
}
if(pulse)
{
output_high(PWM_PIN);
pulse--;
}
else
{
output_low(PWM_PIN);
}
}
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The problem is that, it generates a 11.63 HZ signal and I am unable to increase the frequency.
Please suggest a solution. Thanks in advance. |
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temtronic
Joined: 01 Jul 2010
Posts: 9162
Location: Greensville,Ontario
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| Posted: Sun Oct 31, 2010 2:39 pm |
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Your 11.64 hz is 1/4 that of the 46.5 that you want..so... it's probably in the 'fuses' configuration or setup that is wrong..off by a factor of 4.
I don't use the 18 series but others may know the corect config which may depend upon the version of the compiler... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Oct 31, 2010 2:55 pm |
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| Quote: | #include<18f4520.h> //Device Header
#fuses H4,NOPROTECT,NOWDT,PUT // Set Fuses
#use delay(clock=2000000) //20Mhz Clock
#use RS232 (baud=9600, parity = N, xmit = PIN_C6, rcv=PIN_C7)
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Your #use delay() statement doesn't have 20 MHz in it. It has a smaller
number. Also, the 'H4' fuse is normally used with a 10 MHz crystal to
run the PIC at 40 MHz. 'H4' means the 4x PLL is enabled in the PIC.
This is the maximum speed of the 18F452.
If you have a 20 MHz crystal and you want to run the PIC at 20 MHz,
then use the 'HS' fuse, and edit the #use delay() so it says 20 MHz. |
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