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ccole
Joined: 29 Dec 2009
Posts: 3
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| chip reset timing problems |
 Posted: Tue Dec 29, 2009 10:06 am |
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Hello all, I have a very simple test program written for a 16f877:
| Code: |
#include <16F877.h>
#device ICD=TRUE
#device *=16
#use delay(clock=20000000)
#fuses HS,NOWDT,NOPROTECT,NOLVP,PUT,NOBROWNOUT
#use spi(DI=PIN_C5, DO=PIN_C4, CLK=PIN_C3)
float loalarm = 0;
void print_string(char string[])
{ ... }
void run_setup()
{
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_spi(SPI_MASTER|SPI_MODE_0| SPI_CLK_DIV_16);
output_high(PIN_B4);
delay_ms(10);
if (read_eeprom(0) == 0xFF)
loalarm = 0;
else
loalarm = read_float_from_eeprom(0);
}
void main()
{
char foo[5]={"1010"}
run_setup();
while(TRUE)
print_string(foo);
}
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Nothing too fancy. The read_float_from_eeprom function was taken from here http://www.ccsinfo.com/forum/viewtopic.php?t=32722&start=1
The code works properly until I start to reset the power, and I'm not even resetting it fast. When it powers on, my led display that normally prints 1010 now prints garbage. I need a way to delay the chip from running until the oscillator and the power supply have settled but I haven't been able to figure it out. I tried using setup_oscillator(), but the compiler didn't recognize it. Much thanks in advance!!! |
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Ttelmah
Guest
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| Posted: Tue Dec 29, 2009 11:22 am |
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How is MCLR generated on the chip?. What time constant is involved in this?. What reservoir capacitance is present on the supply?. What loads are present?. How is the ICD powered?.
Have you tried enabling 'brownout'?.
I'd suspect that what is happening, is that your supply is dropping reasonably quickly, into the 'brownout' region, and is then dropping much more slowly, as some circuitry switches off. When you re-apply the supply, sections of the circuitry (possibly including the PIC), have not actually reset.
As far as the PIC is concerned, this is what 'BROWNOUT' is for. So the first thing is to try enabling this.
There is a separate 'issue', that some ICD setups, can supply sufficient power, that they prevent the circuitry fully switching off. Does the same thing happen without ICD?.
Best Wishes |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Dec 29, 2009 1:45 pm |
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| Quote: | #include <16F877.h>
#device ICD=TRUE
#device *=16
#use delay(clock=20000000)
#fuses HS,NOWDT,NOPROTECT,NOLVP,PUT,NOBROWNOUT
#use spi(DI=PIN_C5, DO=PIN_C4, CLK=PIN_C3)
void run_setup()
{
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_spi(SPI_MASTER|SPI_MODE_0| SPI_CLK_DIV_16); |
Also, here you are trying to mix the two methods of setting up the SPI.
Don't do that. My advice is to use the setup_spi() method. It's easier
and less buggy. Then you can use spi_write() and spi_read() to
do SPI operations. There are many examples in the forum archives
of using this method to talk to SPI slave chips with the PIC. |
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ccole
Joined: 29 Dec 2009
Posts: 3
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| Posted: Wed Dec 30, 2009 12:11 pm |
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| Thanks for the replies guys. It looks like when I power cycle quickly, it latches on to the last output on the led display and then the processor doesn't execute anymore instructions....after reading the pic datasheet, it looks like it is powering up in "sleep" mode. Is there any way I can keep it from sleeping? I read some code examples (and tried some) to try to enable an interrupt to wake up the processor (off of timer0) from sleeping on a power up, but nothing seems to work... I'm somewhat stumped again, anybody have experience with processors powering on in sleep mode? |
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ccole
Joined: 29 Dec 2009
Posts: 3
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| Posted: Wed Dec 30, 2009 12:15 pm |
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| also, somewhat confused about the "INT_EXT" interrupts...what can trigger those? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Dec 30, 2009 12:18 pm |
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They don't power-up in sleep mode. If your oscillator circuit is incorrect,
the oscillator might not be running. Or, if you let the program run off
the end of main, then it will go to sleep. Or, if you run the PIC at 3.3v
and enable the Brownout fuse (on the 16F877), then the PIC will be
held in reset permanently.
Try a simple test program to blink an LED on pin B0:
| Code: |
#include <16F877.H>
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 20000000)
//===================================
void main()
{
while(1)
{
output_high(PIN_B0); // Blink LED on pin B0
delay_ms(500);
output_low(PIN_B0);
delay_ms(500);
}
}
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