I developed the following program to interface between the MSP430G2553 on the launchpad and a DS18B20. The VCC and ground of the sensor is connected to the same on the launch pad, and pin2 of the sensor is connect through a 4.7Kohm to Vcc.
The owReadByte() function is always returning 0xFF. Using a USB oscilloscope, the owReset() function works properly, and the sensor pulls the line down to indicate its presence. The write waveform generated looks fine to me too. However, I am missing a response back from the sensor to verify that my write commands were accepted by the sensor.
Appreciate your support.
Update: Now the code is working a delay was missing in the owReset function
Thank you.
#include "msp430g2553.h"
#define OW_IN P1IN
#define OW_OUT P1OUT
#define OW_DIR P1DIR
#define OW_PIN BIT0
unsigned char scratchpad[10],i;
//------------------------------------------------------------------------------
// micro seconds delays
//
void usdelay(int interval){
// Setup TimerA
TACCTL0 = CCIE; // interrupt enabled
TACCR0 = TAR + interval*8; // micro secs @ 8Mhz Clock
TA0CTL = TASSEL_2 + MC_2; // SMCLK, continuous mode.
LPM0; // suspend CPU
}
/*
* This function generates the reset pulse and check for 1-wire device presence. If found, it retuns 1, else return 0
*/
int owReset(void){
int lineState;
OW_OUT &= ~OW_PIN; // Set P1.0 low
OW_DIR |= OW_PIN; // P1.0 output
usdelay(480); // H
OW_DIR &= ~OW_PIN; // Release the bus, it will float to high due to the pull-up resistor.
usdelay(70); // I
lineState = OW_IN & OW_PIN; // Sample input
usdelay(300); // slave TX presence pulse 60-240us
// This delay was missing, and without it, the further write and read were failing
if (lineState == 1){
return (1);
} else {
return (0);
}
}
/*
* READ_BIT - reads a bit from the one-wire bus.
*/
unsigned char owReadBit(void){
unsigned char lineState;
OW_OUT &= ~OW_PIN; // pull pin low to start timeslot
OW_DIR |= OW_PIN; // P1.0 output
usdelay(6); // A=6us but we cannot make it that short.
// Change pin to input waiting for slave to put the data
OW_DIR &= ~OW_PIN; // Release the bus, the line will go high as it is pulled up to Vcc by a resistor
usdelay(10); // Wait E=9us
lineState = OW_IN & OW_PIN; // Sample input to read a bit
usdelay(55); // F=55us to complete the read slot
return (lineState);
}
/*
* WRITE_BIT - writes a bit to the one-wire bus, passed in bitval.
*/
void owWriteBit(char bitval)
{
OW_OUT &= ~OW_PIN; // Set P1.0 low
OW_DIR |= OW_PIN; // P1.0 output
usdelay(6); // A=6us but we cannot make it that short.
if(bitval==1){
OW_DIR &= ~OW_PIN; // P1.0 input, release the bus
usdelay(64); // B
} else {
usdelay(50); // C-A = 60-10=50
OW_DIR &= ~OW_PIN; // P1.0 input, release the bus
usdelay(10); // D
}
}
/*
* READ_BYTE - reads a byte from the one-wire bus.
*/
unsigned char owReadByte(void){
unsigned char i;
unsigned char value = 0;
for (i=0;i<8;i++) {
if(owReadBit()){
value|=0x01<<i; // reads byte in, one bit at a time and then shifts it left
}
}
return(value);
}
/*
* WRITE_BYTE - writes a byte to the one-wire bus.
*/
void owWriteByte(char val){
unsigned char i;
unsigned char temp;
for (i=0; i<8; i++) { // writes byte, one bit at a time
temp = val>>i; // shifts val right 'i' spaces
temp &= 0x01; // copy that bit to temp
owWriteBit(temp); // write bit in temp into
}
}
void main(void)
{
WDTCTL = WDTPW + WDTTMSEL; // WDT as interval timer,
// f = SMCLK / 32768
//Calibrate DCO for 8MHz operation
BCSCTL1 = CALBC1_8MHZ;
DCOCTL = CALDCO_8MHZ;
__enable_interrupt(); // Enable global interrupt
/*
* Reset, Skip ROM, Convert T, Wait for 750us, Reset, Skip ROM, Read Scratchpad, Master loops a read slot to
* receive data from the device LSB First
*/
owReset(); // Check device presence
owWriteByte(0xcc); // Skip ROM
owWriteByte(0x44); // Convert Temperature
usdelay(1000);
owReset(); // Check device presence
owWriteByte(0xcc); // Skip ROM
owWriteByte(0xbe); // Read Scratchpad
for (i=0; i<8; i++) { // writes byte, one bit at a time
scratchpad[i]= owReadByte();
}
owReset(); // Stop reading
LPM0;
}
// Timer A0 interrupt service routine. TIMERx_Ay_VECTOR.(x being the index of the timer, y of the vector for this timer)
#pragma vector=TIMER0_A0_VECTOR
__interrupt void Timer_A0 (void)
{
TA0CTL = 0; // Stop Timer_A
LPM0_EXIT; // Return active
}
