/*

***********************************************************************************************

* SHT1x digital temperature and humidity sensor Driver

* All Rights Reserved

* File name : SHT1x.c

* Programmer : John Leung, TechToys Co. Hong Kong

* Web presence : www.TechToys.com.hk

* Downloaded from www.microchipc.com - see site for more sample PIC C code

* Note :

* Language : C18 complier version 2.40, MPLAB v7.41

* Hardware : PIC18LF4550-STK1

* Date : 11 Oct 2006 Version 1.0

***********************************************************************************************

* DESCRIPTION

*

* This module provides an interface to Sensirion SHT10 digital temperature & humidity sensor

*

* pinout function summarized as below

* ---SHT1x MCU -----------------

* DATA - data RA2

* SCK - clock RA0

***********************************************************************************************

*/

#include <p18cxxx.h>

#include "SHT1x.h"

#include "delay.h"

/*

*********************************************************************************************************

* LOCAL DEFINITIONS

*********************************************************************************************************

*/

//adr command r/w

#define STATUS_REG_W 0x06 //000 0011 0

#define STATUS_REG_R 0x07 //000 0011 1

#define MEASURE_TEMP 0x03 //000 0001 1

#define MEASURE_HUMI 0x05 //000 0010 1

#define RESET 0x1e //000 1111 0

#define noACK 0

#define ACK 1

/*

*********************************************************************************************************

* SOFT RESET THE SENSOR

*

* Description : Soft reset, resets the interface, clears the status register to default values

* Wait minimum 11 ms before next command

* Arguments : none

*

* Returns : 1 if no response from the sensor

* Notes :

*********************************************************************************************************

*/

char s_softreset(void)

{

unsigned char error=0;

s_connectionreset(); //reset communication

error+=s_write_byte(RESET); //send RESET-command to sensor

return error; //error=1 in case of no response from the sensor

}

/*

*********************************************************************************************************

* MAKE MEASUREMENT ON HUMIDITY AND TEMPERATURE IN 12BITS ADN 14BITS

*

* Description : Makes a measurement (humidity/temperature) with checksum

* Arguments :

*

* Returns :

* Notes : It takes approximately 11/55/210 ms for a 8/12/14bit measurement.

* Measurement data is stored until readout.

* Two bytes of measurement data and one byte of CRC checksum will then be transmitted.

* The uC must acknowledge each byte by pulling the DATA line low.

*********************************************************************************************************

*/

char s_measure(unsigned char *p_value, unsigned char *p_checksum, unsigned char mode)

{

unsigned error=0;

unsigned int i;

s_transstart(); //transmission start

switch(mode){ //send command to sensor

case TEMP : error+=s_write_byte(MEASURE_TEMP); break;

case HUMI : error+=s_write_byte(MEASURE_HUMI); break;

default : break;

}

(mode==HUMI)?DelayMs(55):DelayMs(210);

for (i=0;i<65535;i++) if(DATA_RD==0) break; //wait until sensor has finished the measurement

if(DATA_RD) error+=1; //or timeout (~2 sec.) is reached

*(p_value+1) = s_read_byte(ACK); //read the first byte (MSB)

*(p_value) = s_read_byte(ACK); //read the second byte (LSB)

*p_checksum = s_read_byte(noACK); //read checksum

return error;

}

/*

*********************************************************************************************************

* TRANSMISSION START SEQUENCE

*

* Description : To initiate a transmission, a “Transmission Start?sequence has to be issued.

* Arguments : none

*

* Returns : none

* Notes :

* generates a transmission start

* _____ ________

* DATA: |_______|

* ___ ___

* SCK : ___| |___| |______

*********************************************************************************************************

*/

void s_transstart(void)

{

SCK=0; //Initial state

DATA_TRIS = 1; //pullup resistor brings DATA pin high

DelayUs(1);

SCK=1;

DelayUs(1);

DATA_WR=0; DATA_TRIS=0;

DelayUs(1);

SCK=0;

DelayUs(5);

SCK=1;

DelayUs(1);

DATA_TRIS=1; //pullup resistor brings DATA pin high

DelayUs(1);

SCK=0;

}

/*

*********************************************************************************************************

* CONNECTION RESET SEQUENCE

*

* Description : This sequence resets the interface only. The status register preserves its content.

* Arguments : none

*

* Returns : none

* Notes :

* communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart

* _____________________________________________________ ________

* DATA: |_______|

* _ _ _ _ _ _ _ _ _ ___ ___

* SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______

*********************************************************************************************************

*/

void s_connectionreset(void)

{

unsigned char i;

DATA_WR = 1; //set data pin high

DATA_TRIS = 0; //set data pin an output

SCK = 0;

SCK_TRIS = 0; //set CLK pin an output low

for(i=0;i<9;i++) //9 SCK cycles for connection reset sequence

{ SCK=1;

DelayUs(1);

SCK=0;

DelayUs(1);

}

s_transstart(); //transmission start

}

/*

*********************************************************************************************************

* LOW LEVEL READ FUNCTION

*

* Description : Read a byte form the Sensibus and gives an acknowledge in case of "ack == ACK"

* Arguments : 'ack' ACK (1) if acknowledge required

* noACK (0) in case acknowledge NOT required

*

* Returns : return the byte read from the sensor

* Notes :

*********************************************************************************************************

*/

char s_read_byte(unsigned char ack)

{

unsigned char i,val=0;

DATA_TRIS = 1; //set DATA line an input

SCK = 0;

for (i=0x80;i>0;i/=2) //shift bit for masking

{ SCK=1; //clk for SENSI-BUS

DelayUs(2);

if (DATA_RD) val=(val | i); //read bit

SCK=0;

DelayUs(2);

}

if(ack==ACK)

{

DATA_TRIS = 0;

DATA_WR = 0;

}

SCK=1; //clk #9 for ack

DelayUs(5); //pulse-width approx. 5 us

SCK=0;

DATA_TRIS = 1; //release DATA-line

return val;

}

/*

*********************************************************************************************************

* LOW LEVEL WRITE FUNCTION

*

* Description : Write a byte on the Sensibus and checks the acknowledge

* Arguments : 'value' is the byte to write to the sensor

*

* Returns : 1 in case of an error (no acknowledge) from the sensor

* Notes :

*********************************************************************************************************

*/

char s_write_byte(unsigned char value)

{

unsigned char i,error=0;

DATA_TRIS = 0;

for (i=0x80;i>0;i/=2) //shift bit for masking

{ if (i & value) DATA_WR=1; //masking value with i , write to SENSI-BUS

else DATA_WR=0;

SCK=1; //clk for SENSI-BUS

DelayUs(5); //pulse-width approx. 5 us

SCK=0;

DelayUs(5);

}

DATA_TRIS=1; //release DATA-line, let SHT10 sensor controls DATA line

SCK=1; //clk #9 for ack

error=DATA_RD; //check ack (DATA will be pulled down by SHT11)

SCK=0;

return error; //error=1 in case of no acknowledge

}