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Message |
ice
Joined: 30 May 2005
Posts: 10
Location: India
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| delay_us() problem |
 Posted: Sun Feb 04, 2007 12:18 pm |
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Hello,
i'm running a 16F876A chip at 20Mhz
I am trying to drive a hobby servo, using the following code(from elsewhere in this forum) to generate 1ms to 2ms timings.
| Code: |
#include <16F876A.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#define quar_mov 100
#int_TIMER0 // This function is called every time
void servo_isr() // the RTCC (timer0) overflows (255->0).
{
int b=10;
output_high(PIN_C0);
delay_ms(1);
delay_us(quar_mov*b);
output_low(PIN_C0);
}
void main()
{
set_timer0(0);
setup_timer_0( RTCC_INTERNAL | RTCC_DIV_256 );
enable_interrupts(INT_TIMER0);
enable_interrupts(GLOBAL);
while(1);
}
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I need to keep updating the value of "b" from a scale (0 to 10) to generate 1ms to 2ms delays.
According to the manual,
Syntax: delay_us (time)
Parameters: time - a variable 0-255 or a constant 0-65535
if I key in delay_us(100*10), it gives a perfect 1ms delay.
But delay_us(quar_mov*b); gives me less than 1ms.
Please note that delay_us(quar_mov*10) also gives a perfect 1ms delay.
It's the int b which is not getting loaded in.
Is there any work around this?
Thank you.
_________________
**ice**
Machinegrid.com :: Robots at Work!! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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ice
Joined: 30 May 2005
Posts: 10
Location: India
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| Thank you |
| Posted: Sun Feb 04, 2007 1:12 pm |
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Thank you for your help,PCM.
It now works.
My servo update in now at 70Hz ,I 'm not able to go lower than that(RTCC_DIV_256).It's slow, but it gets it's position right.
In case anyone finds it useful, hobby servo control code:
| Code: |
#include <16F876A.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
void long_delay_ms(long count)
{
long k;
for(k = 0; k <count>0).
{
int16 sum;
int16 b=20;
output_high(PIN_C0);
sum=400+(b*20); //change value of b from 0 to 20(1ms to 2ms)
long_delay_ms(sum); // 400 for 1ms,,600 for 1.5ms,800 for 2ms
output_low(PIN_C0);
}
void main()
{
set_timer0(0);
setup_timer_0( RTCC_INTERNAL | RTCC_DIV_256 );
enable_interrupts(INT_TIMER0);
enable_interrupts(GLOBAL);
while(1);
}
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