// msp430G2553 i2c bus <-> Si7021 humidity & temperature sensor

 // pullup resistors for SDA & SCL lines: 10kOhm

 // jumper for LED2 should be removed, or I2C bus won't work.

 #include "io430.h"

 #include "TI_USCI_I2C_master.h"

 #define SI7021_ADDRESS 0x40

 #define MEASURE_RH_HOLD 0xE5

 #define MEASURE_RH_NO_HOLD 0xF5

 #define READ_T_FROM_PRE_RH_MEASUREMENT 0xE0

 #define RXD BIT1 //P1.1

 #define TXD BIT2 //P1.2

 unsigned char array[] = {};

 unsigned char store[] = {, , };

 unsigned int outHumi = ;

 float valueHumi = 0.0;

 int outTemp = ;

 float valueTemp = 0.0;

 // functions for printf()

 void sendByte(unsigned char);

 void printf(char *, ...);

 void initUART(void);

 void printf_f(float);

 void main( void )

 {

     // Stop watchdog timer to prevent time out reset

     WDTCTL = WDTPW + WDTHOLD;

     // DCO setup

     BCSCTL1 = CALBC1_1MHZ;

     DCOCTL = CALDCO_1MHZ;

     // UART setup

     initUART();

     __enable_interrupt();

     while()

     {

         TI_USCI_I2C_transmitinit(SI7021_ADDRESS, ); // init transmitting with USCI

         // scl clock: f(BRCLK)/10; BRCLK <- SMCLK

         while(TI_USCI_I2C_notready()); // wait for bus to be free

         array[] = MEASURE_RH_NO_HOLD;

         TI_USCI_I2C_transmit(, array);

         while(TI_USCI_I2C_notready());

         __delay_cycles(); //delay 25ms

         // get the humidity result

         TI_USCI_I2C_receiveinit(SI7021_ADDRESS, );

         while(TI_USCI_I2C_notready());

         TI_USCI_I2C_receive(,store);

         while(TI_USCI_I2C_notready()); 

         outHumi = (store[]<<) | store[];

         valueHumi = 125.0*outHumi/ - ;

         //printf("heX            %x\r\n", outHumi);

         //printf("heX            %x\r\n", (unsigned int)store[2]);

         //printf("Integer        %i\r\n", (int)valueHumi);

         printf_f(valueHumi);

         printf(" %%RH   ");

         // get temperature from previous RH measurement

         TI_USCI_I2C_transmitinit(SI7021_ADDRESS, );

         while(TI_USCI_I2C_notready());

         array[] = READ_T_FROM_PRE_RH_MEASUREMENT;

         TI_USCI_I2C_transmit(, array);

         while(TI_USCI_I2C_notready());

         TI_USCI_I2C_receiveinit(SI7021_ADDRESS, ); // init receiving with USCI

         while(TI_USCI_I2C_notready()); // wait for bus to be free

         TI_USCI_I2C_receive(,store);

         while(TI_USCI_I2C_notready()); 

         outTemp = (store[]<<) | store[];

         valueTemp = 175.72*outTemp/ - 46.85;     

         //printf("heX            %x\r\n", outTemp);

         //printf("Integer        %i\r\n", (int)valueTemp);

         printf_f(valueTemp);

         printf(" `C\r\n");

         __delay_cycles(); //delay 2s

     }

 }

 void initUART(void) {

     //config P1.1 RXD, P1.2 TXD

     P1SEL |= TXD + RXD;

     P1SEL2 |= TXD + RXD;

     //reset UCA0, to be configured

     UCA0CTL1 = UCSWRST;

     //config

     UCA0CTL1 |= UCSSEL_2; //SMCLK

     UCA0BR0 = ;

     UCA0BR1 = ;//1MHz baut rate = 9600

     UCA0MCTL = UCBRS0; // Modulation UCBRSx = 1

     //make UCA0 out of reset

     UCA0CTL1 &= ~UCSWRST;

 }

 void sendByte(unsigned char byte )

 {

     while (!(IFG2&UCA0TXIFG));            // USCI_A0 TX buffer ready?

     UCA0TXBUF = byte;                // TX -> RXed character

 }

 void printf_f(float fnumber)

 {

     int ipart = (int)fnumber; // integer part

     int fpart = (int)((fnumber - ipart)*); //fractional part, 2 decimal places

     printf("%i.", ipart);

     if(fpart<)

     {

         fpart = -fpart;

     }

     if(fpart<)

     {

         printf("");

     }

     printf("%i", fpart);

 }