PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Sun Mar 14, 2010 1:22 pm |
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Here's the complete test program for the ds18B20 in parasite-power
mode. This is the original poster's program, with the modifications
added, that I recommended in a post above. I'm posting the integrated
program because of a request.
| Code: |
#include <16F877.H>
#fuses XT, NOWDT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#define DQ PIN_C2
//-------------------------------------
void ow_reset(void)
{
output_low(DQ);
delay_us(500); // Min. 480uS
output_float(DQ);
delay_us(500); // Wait for end of timeslot
}
//-------------------------------------
// Read bit on one wire bus
int8 read_bit(void)
{
output_low(DQ);
delay_us(1);
output_float(DQ);
delay_us(12); // Read within 15uS from start of time slot
return(input(DQ));
}
//-------------------------------------
int8 read_byte(void)
{
int8 i;
int8 val = 0;
for(i=0 ; i<8 ; i++)
{
if(read_bit()) val |= (0x01 << i);
delay_us(120); // To finish time slot
}
return val;
}
//-------------------------------------
void write_byte(int8 val, int8 power_on)
{
int i;
for(i=0; i<8; i++)
{
output_low(DQ);
delay_us( 2 );
output_bit(DQ, shift_right(&val,1,0));
delay_us(60);
if((i == 7) && (power_on == 1))
{
output_high(DQ);
}
else
{
output_float(DQ);
delay_us( 2 );
}
}
}
//==========================================
void main(void)
{
int8 i;
signed int16 temperature;
int8 scratch[9];
output_float(DQ);
while(1)
{
ow_reset();
write_byte(0xCC, 0); // Skip Rom command
write_byte(0x44, 1); // Temperature Convert command
delay_ms(750); // Max. time for conversion is 750mS
ow_reset();
write_byte(0xCC, 0); // Skip Rom command
write_byte(0xBE, 0); // Read scratch pad command
// Get the data bytes
for(i=0; i < 8; i++)
{
scratch[i] = read_byte();
}
ow_reset();
temperature = (signed int16) make16(scratch[1],scratch[0]);
if(temperature >= 0)
temperature = (temperature + 8)/16;
else
temperature = (temperature - 8)/16;
printf("Temp: %4Ld C \n\r",temperature);
}
} |
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