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homfray
Joined: 19 Nov 2003
Posts: 45
Location: Oxford
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| EX_GLINT.C what sets the time of the interupt |
 Posted: Fri Dec 19, 2003 9:51 am |
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 Soory know its a bit of thick question. What sets the interupt time in the EX_GLINT example I know the interupt must be set to interupt every two seconds-ish
thanks
dvae |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Dec 19, 2003 3:03 pm |
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The frequency is set by this line:
setup_counters(RTCC_INTERNAL,RTCC_DIV_32);
and also, it's determined by the crystal frequency (divided by 4).
In addition, it's set by the size of Timer0. In the 16F series PICs,
Timer0 is 8 bits. In the 18F series it can be configured as 8 or 16 bits.
So instead of having 256 counts per interrupt, if it was configured
for 16-bits, it would take 65536 counts. |
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homfray
Joined: 19 Nov 2003
Posts: 45
Location: Oxford
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| Posted: Tue Dec 23, 2003 4:58 am |
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So in the ex_glint code I would change
| Code: | long counter;
int save_w;
#locate save_w=0x80
int save_status;
#locate save_status=0xFF
#byte status = 0xFD8
#bit zero_flag = status.2
#bit t0if = 0xFF2.2 |
#bit t0if = 0xFF2.2 is it this section that i change
I am still unsure I can see that the setup counter will change the timing such that it is a quater of the clock cycle and that the setup_counters(RTCC_INTERNAL,RTCC_DIV_32); is a 32nd of that. But where do I add a number to count down from
I changed
#bit t0if = 0xFF2.2
to
#bit t0if = 0x222.2
and all it seemed to do was make my code not run properly |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Dec 23, 2003 2:11 pm |
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Tell us exactly what you want to do.
If you want to change interrupt rate, then what rate do you want ? |
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homfray
Joined: 19 Nov 2003
Posts: 45
Location: Oxford
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| Posted: Wed Dec 24, 2003 2:45 am |
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I would like to have see how you would set an interupt
every millisecond
and an interupt every half second these two should give me the knowledge to see how to adjust the code to change set the interupt time
I am using a 4MHz clock |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Dec 28, 2003 3:08 pm |
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Here is the example you requested.
It contains code to setup the RTCC (Timer 0) for either 1000 Hz or 2 Hz.
To test one frequency, you have to comment out the code for the
other frequency. It's currently setup for 1000 Hz. Be aware that
in the 18F458 and similar chips, the default size of Timer 0 is 16-bits.
ie., it counts from 0 to 65535, and then rolls over to 0. In the example
below, it is configured as a 16-bit counter.
This code doesn't compensate for interrupt latency, so at a low
crystal frequency of 4 MHz, the frequency of the signal on pin B1
will be off somewhat (about 5% low, on the 1000 Hz signal).
But this is a beginners example, and you can learn about
adjusting for latency later.
| Code: | #include <18F458.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 4000000)
//#use rs232(baud = 9600, xmit=PIN_C6, rcv = PIN_C7, ERRORS)
#int_rtcc
void int_rtcc_isr(void)
{
static short state = 0;
//set_timer0(34286); // 2 Hz reload value (pre-scaler = 16)
set_timer0(64536); // 1000 Hz reload value (pre-scaler = 1)
// Output the current state on pin B1, and then
// toggle it to the opposite value for the next interrupt.
// On the oscilloscope, you will see a 500 Hz
// squarewave, or a 1 Hz squarewave.
output_bit(PIN_B1, state);
state = ~state;
}
//===========================================
void main()
{
output_low(PIN_B1); // Initialize Pin B1 to a low level
// Setup the RTCC to interrupt at a rate of 2 Hz.
//setup_counters(RTCC_INTERNAL, RTCC_DIV_16);
//set_timer0(34286);
// Setup the RTCC to interrupt at a rate of 1000 Hz.
setup_counters(RTCC_INTERNAL, RTCC_DIV_1);
set_timer0(64536);
enable_interrupts(INT_RTCC);
enable_interrupts(GLOBAL);
while(1);
} |
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