Page 11 of 21
Chapter 14
Page 233
#include <bcm2835.h>
#include <stdio.h>
int presence(uint8_t pin);
void writeBit(uint8_t pin, int b);
void writeByte(uint8_t pin, int byte);
uint8_t readBit(uint8_t pin);
int convert(uint8_t pin);
int readByte(uint8_t pin);
float getTemperature(uint8_t pin);
uint8_t crc8(uint8_t *data, uint8_t len);
int main(int argc, char **argv)
{
if (!bcm2835_init())
return 1;
if (presence(RPI_BPLUS_GPIO_J8_07) == 1)
{
printf("No device \n");
}
else
{
printf("Device present \n");
}
fflush(stdout);
float t;
for (;;)
{
do
{
t = getTemperature(RPI_BPLUS_GPIO_J8_07);
} while (t < -999);
printf("%f\r\n", t);
fflush(stdout);
};
bcm2835_close();
return 0;
}
int presence(uint8_t pin)
{
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
bcm2835_gpio_write(pin, LOW);
bcm2835_delayMicroseconds(480);
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);
bcm2835_delayMicroseconds(70);
uint8_t b = bcm2835_gpio_lev(pin);
bcm2835_delayMicroseconds(410);
return b;
}
void writeBit(uint8_t pin, int b)
{
int delay1, delay2;
if (b == 1)
{
delay1 = 6;
delay2 = 64;
}
else
{
delay1 = 60;
delay2 = 10;
}
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
bcm2835_gpio_write(pin, LOW);
bcm2835_delayMicroseconds(delay1);
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);
bcm2835_delayMicroseconds(delay2);
}
void writeByte(uint8_t pin, int byte)
{
int i;
for (i = 0; i < 8; i++)
{
if (byte & 1)
{
writeBit(pin, 1);
}
else
{
writeBit(pin, 0);
}
byte = byte >> 1;
}
}
uint8_t readBit(uint8_t pin)
{
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
bcm2835_gpio_write(pin, LOW);
bcm2835_delayMicroseconds(8);
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);
bcm2835_delayMicroseconds(2);
uint8_t b = bcm2835_gpio_lev(pin);
bcm2835_delayMicroseconds(60);
return b;
}
int convert(uint8_t pin)
{
int i;
writeByte(pin, 0x44);
for (i = 0; i < 5000; i++)
{
bcm2835_delayMicroseconds(100000);
if (readBit(pin) == 1)
break;
}
return i;
}
float getTemperature(uint8_t pin)
{
if (presence(pin) == 1)
return -1000;
writeByte(pin, 0xCC);
if (convert(pin) == 5000)
return -3000;
presence(pin);
writeByte(pin, 0xCC);
writeByte(pin, 0xBE);
int i;
uint8_t data[9];
for (i = 0; i < 9; i++)
{
data[i] = readByte(pin);
}
uint8_t crc = crc8(data, 9);
if (crc != 0)
return -2000;
int t1 = data[0];
int t2 = data[1];
int16_t temp1 = (t2 << 8 | t1);
float temp = (float)temp1 / 16;
return temp;
}
int readByte(uint8_t pin)
{
int byte = 0;
int i;
for (i = 0; i < 8; i++)
{
byte = byte | readBit(pin) << i;
};
return byte;
}
uint8_t crc8(uint8_t *data, uint8_t len)
{
uint8_t i;
uint8_t j;
uint8_t temp;
uint8_t databyte;
uint8_t crc = 0;
for (i = 0; i < len; i++)
{
databyte = data[i];
for (j = 0; j < 8; j++)
{
temp = (crc ^ databyte) & 0x01;
crc >>= 1;
if (temp)
crc ^= 0x8C;
databyte >>= 1;
}
}
return crc;
}
