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Patronus
Joined: 05 Jun 2012
Posts: 10
Location: Sri Lanka
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| Using Timer1 of 16F877A to count seconds |
 Posted: Tue Jun 12, 2012 10:48 am |
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I want to count seconds using timer1 of 16F877A. I used 4 as the prescaler. So the number of interrupts per second = 20000000/(4x4x65536).
To check whether this works, I wrote the following code.
| Code: |
#include <16F877A.h>
#device adc=10
#FUSES NOWDT //No Watch Dog Timer
#FUSES HS //High speed Osc (> 4mhz)
#FUSES NOPUT //No Power Up Timer
#FUSES NOPROTECT //Code not protected from reading
#FUSES NODEBUG //No Debug mode for ICD
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOLVP //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOCPD //No EE protection
#FUSES NOWRT //Program memory not write protected
#use delay(clock=20000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8)
#define INTS_PER_SECOND 19 // (20000000/(4*4*65536))
int int_count; // Number of interrupts left before a second has elapsed
int16 seconds = 0;
void setTimer()
{
OUTPUT_HIGH(PIN_B5);
int_count=INTS_PER_SECOND;
set_timer1(0);
setup_timer_1(T1_INTERNAL | T1_DIV_BY_4);
}
#int_timer1
void clock_isr() {
if(--int_count==0)
{
++seconds;
int_count=INTS_PER_SECOND;
}
}
void main()
{
setup_adc_ports(AN0);
setup_adc(ADC_CLOCK_DIV_32);
setup_psp(PSP_DISABLED);
setup_spi(FALSE);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_256);
setup_timer_1(T1_INTERNAL | T1_DIV_BY_4);
setup_timer_2(T2_DISABLED,0,1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
enable_interrupts(INT_RTCC);
enable_interrupts(GLOBAL);
enable_interrupts(INT_TIMER1);
OUTPUT_B(0);
SET_TRIS_B(10000000);
setTimer();
while(1)
{
while(seconds==1)
{
OUTPUT_HIGH(PIN_B1);
}
}
} |
But I can't see PIN_B1 becoming high when a second is elapsed.
I used this very same code to count seconds using timer0 and it worked.
Can someone please tell me what's wrong here?
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"Silence is argument carried out by other means" |
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Gabriel
Joined: 03 Aug 2009
Posts: 1067
Location: Panama
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| Posted: Tue Jun 12, 2012 11:07 am |
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you never reset "seconds"... so in order for this to happen:
| Code: | while(seconds==1)
{
OUTPUT_HIGH(PIN_B1);
} |
you will have to wait 254 seconds... EDIT: its a 16bit variable... so 65534 (18+hours)
and then... even when it does happen again... you wont notice.. because you never bring PIN_B1 back low...
as a word of advise... leave TRIS alone... delete that line.
G
_________________
CCS PCM 5.078 & CCS PCH 5.093
Last edited by Gabriel on Tue Jun 12, 2012 11:16 am; edited 2 times in total |
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Gabriel
Joined: 03 Aug 2009
Posts: 1067
Location: Panama
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| Posted: Tue Jun 12, 2012 11:11 am |
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| Code: | #int_timer1
void clock_isr() {
if(--int_count==0)
{
TOGGLE_PIN(PIN_B1) <------------- that would be better.
int_count=INTS_PER_SECOND;
}
} |
if your timing is correct... you should se a ~1Hz output signal on B1.
_________________
CCS PCM 5.078 & CCS PCH 5.093 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Jun 12, 2012 11:35 am |
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| Quote: |
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_256);
enable_interrupts(INT_RTCC);
enable_interrupts(GLOBAL);
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Where is your #int_rtcc routine ?
| Quote: | SET_TRIS_B(10000000);
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What's the default number base used by the C language ? |
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Patronus
Joined: 05 Jun 2012
Posts: 10
Location: Sri Lanka
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| Posted: Tue Jun 12, 2012 11:51 am |
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Gabriel,
Thanks for the reply.
yeah, checking it inside isr is better. Anyway I don't get a 1Hz output signal..
When my program runs, at the beginning timer is set and when number of interrupts that occurred becomes 19, the variable "seconds" should increment from 0 to 1.
What's wrong with the logic there? Why 254 seconds?
PCM Programmer,
I'm sorry, I just used the code that I used to check timer0 and that's why those lines are still there. As I know the least significant bit is for B0.
_________________
"Silence is argument carried out by other means" |
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Patronus
Joined: 05 Jun 2012
Posts: 10
Location: Sri Lanka
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| Posted: Tue Jun 12, 2012 12:05 pm |
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Hello PCM Programmer... if I either add #int_rtcc routine or remove
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_256);
enable_interrupts(INT_RTCC);
lines, the code works..
That was the problem I guess..?
Thanks a lot..
_________________
"Silence is argument carried out by other means" |
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Gabriel
Joined: 03 Aug 2009
Posts: 1067
Location: Panama
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| Posted: Tue Jun 12, 2012 12:27 pm |
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| Quote: | When my program runs, at the beginning timer is set and when number of interrupts that occurred becomes 19, the variable "seconds" should increment from 0 to 1.
What's wrong with the logic there? Why 254 seconds? |
Because the statement :
| Code: | while(seconds==1)
{
OUTPUT_HIGH(PIN_B1);
} |
will only happen when seconds = 1.
assume Seconds is =1 ... it goes into the while loop...
your timer keeps going... you have 19 more interrupts and then... seconds becomes 2... then 3 then 4 and so on... only when it overflows and flips over to 0 you will be able to go from 0 to 1... thus the statement will only execute ONCE every "size of Seconds variable" .. in this case its int16 so 65534 times...
Edit:
and like i said ... when it finally does happen... you wont notice it becase PIN_B1 is already high from the last time it did happen.... toggle the pin or set it low after some time before the next time seconds = 1.
_________________
CCS PCM 5.078 & CCS PCH 5.093 |
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Patronus
Joined: 05 Jun 2012
Posts: 10
Location: Sri Lanka
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| Posted: Tue Jun 12, 2012 12:49 pm |
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Gabriel, anyway I should be able to see the first time it happens right? The problem was that I couldn't see that happening. Now after doing what I've mentioned in previous reply, I can see it happening.
_________________
"Silence is argument carried out by other means" |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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Patronus
Joined: 05 Jun 2012
Posts: 10
Location: Sri Lanka
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| Posted: Tue Jun 12, 2012 1:31 pm |
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I'm sorry... I haven't understand the question..
Bad mistake. I'll be more careful.
_________________
"Silence is argument carried out by other means" |
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