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karthickiw
Joined: 09 Aug 2007
Posts: 82
Location: TN, India
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| how to check the BOR bit |
 Posted: Tue Sep 18, 2007 9:47 am |
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sir,
i write the program for write the data in eeprom during power fail time. I check the BOR bit and write the data into the memory but program is store the data during the power on time itself....
program is
| Code: |
#include<16f873a.h>
#device adc=10
#use delay (clock=4000000)
#fuses xt,nowdt,noprotect,noput,nolvp,BROWNOUT
#use rs232(baud=9600,parity=N,xmit=PIN_C7,rcv=PIN_C6,bits=8)
#BYTE PCON_REG=0x8E // BOR address
#BIT BOD_BAR=PCON_REG.0
#BIT POR_BAR=PCON_REG.1
void main()
{
int value;
setup_adc(ADC_CLOCK_INTERNAL);
setup_adc_ports( ALL_ANALOG );
set_adc_channel(1);
while (true) {
delay_ms(200);
value = read_adc();
printf("\f A/D value = %U bor= %u POR= %u", value, BOD_BAR,POR_BAR);
if (BOD_BAR) //check the BOR bit
{
}
else
{
write_eeprom(0,2) ; // power fail time, this line is executed
}
}
}
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[/code] |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Sep 18, 2007 10:53 am |
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It's useless to read the BOR bit, because if Brownout is enabled the PIC
will reset when it hits the BOR voltage. You need a method to
detect the low Vdd voltage, and still allow the main program to keep
running.
If you want to detect the low Vdd voltage internally in the PIC, then
get a PIC that has a LVD module (Low Voltage Detection), such as
the 18F452 or other PICs. Here's some example code to use LVD:
http://www.ccsinfo.com/forum/viewtopic.php?t=24577
You also need the PCH compiler (or PCWH) to compile code for the 18F PICs. |
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karthick.E
Guest
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| thank u |
| Posted: Tue Sep 18, 2007 8:09 pm |
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sir,
pls give any idea to write the process data during power fail time sir... i try RB0 pin interrupt, but RB0 only goes interrupt function voltage is low to high... how detect the high to low interrupts in RB0 of PIC16F873A.. pls give any circuit diagram sir... |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Wed Sep 19, 2007 2:22 am |
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| Quote: | | RB0 only goes interrupt function voltage is low to high... |
Use the function ext_int_edge() to select the edge that should generate the interrupt.
Detecting power supply problems using the interrupt pins is not easy because the trigger level is related to the power supply. So when the supply voltage drops, so does the trigger level and you will never see an interrupt. A way to work around this limitation is when you connect the interrupt pin to a voltage divider that is placed before the voltage regulator of your application.
The PIC16F873A is not the best chip for detecting power supply problems because it has no Low Voltage Detect (LVD) module. Why are you using this chip? For example the PIC16F913 also has 28 pins, has more features including an LVD module, uses less power and is cheaper. |
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