main.cpp

00001 /*
00002  *   NXP LM75B temperature sensor test
00003  *   www.nxp.com/pip/LM75B_2.html
00004  *   
00005  *   Expecting to use the pins 9 and 10 for I2C bus
00006  *   these pins should be pulled-up properly. 
00007  *
00008  *   The temperature read out will be shown on terminal on the PC screen. 
00009  *   
00010  *   In this demo code, two LM75B devices can be driven. 
00011  *   These two devices should have different I2C address setting 
00012  *   using its address pins (LM75B's A0 to A2 (pins 5 to 7)). 
00013  *   One LM75B should have all those pins tied to GND. 
00014  *   And another should have the pin A0(pin7) pulled-up. 
00015  *
00016  *   From the software, those devices can be accessed by I2C addresses 
00017  *   "0x90" and "0x92". 
00018  *   It will not be as "0x90" and "0x91" because the address has 
00019  *   7 bit only and stuffed to left. So the "A0" setting become 0xX2. 
00020  *   The LSB does not care because it will be set by I2C libraly when 
00021  *   it transfer the data for read and write. 
00022  */
00023 
00024 #include "mbed.h"
00025 //#include "SDFileSystem.h"
00026 
00027 //  LM75B IIC address
00028 #define    LM75B_ADDR 0x90
00029 
00030 //  LM75B registers
00031 #define    Conf        0x01
00032 #define    Temp        0x00
00033 #define    Tos         0x03
00034 #define    Thyst       0x02
00035 
00036 
00037 DigitalOut    led[]            = { LED4, LED3, LED2, LED1 };
00038 Serial        pc(USBTX, USBRX); // tx, rx
00039 
00040 I2C           i2c( p9, p10 );        // sda, scl
00041 
00042 
00043 void   iic_write( char addr, char reg, char data );
00044 char   iic_read( char addr, char reg );
00045 short  iic_read_short( char addr, char reg );
00046 void   iic_error( void );
00047 
00048 void   init_temp_sensor( char dev_num );
00049 float  get_temp( char dev_num );
00050 
00051 int main() {
00052     int    i;
00053     
00054     init_temp_sensor( 0 );
00055     init_temp_sensor( 1 );
00056 
00057     while(1) {
00058         pc.printf( "  (%d)  temp[0]=%6.3f, temp[1]=%6.3f(degree-C)\n", i++, get_temp( 0 ), get_temp( 1 ) );
00059         wait( 1 );
00060     }
00061 }
00062 
00063 void init_temp_sensor( char dev_num )
00064 {
00065     dev_num    <<= 1;
00066     
00067     iic_write( LM75B_ADDR | dev_num, Conf, 0x00 );    //    configuration
00068     pc.printf( "sensor[%d] : Conf  register read out = 0x%02X\n", dev_num, iic_read( LM75B_ADDR | dev_num, Conf ) );
00069     pc.printf( "sensor[%d] : Tos   register read out = 0x%04X\n", dev_num, iic_read_short( LM75B_ADDR | dev_num, Tos ) );
00070     pc.printf( "sensor[%d] : Thyst register read out = 0x%04X\n", dev_num, iic_read_short( LM75B_ADDR | dev_num, Thyst ) );
00071 }
00072 
00073 
00074 float get_temp( char dev_num )
00075 {
00076     dev_num    <<= 1;
00077 
00078     return ( (float)(iic_read_short( LM75B_ADDR | dev_num, Temp )) / 256.0 );
00079 }
00080 
00081 void iic_write( char addr, char reg, char data )
00082 {
00083     char cmd[2];
00084     
00085     cmd[ 0 ]    = reg;
00086     cmd[ 1 ]    = data;
00087     
00088     if ( i2c.write( addr, cmd, 2) )
00089         iic_error();        
00090 }
00091 
00092 char iic_read( char addr, char reg )
00093 {
00094     char cmd;
00095     int nack;
00096 
00097     cmd    = reg;
00098    
00099     nack     = i2c.write( addr, &cmd, 1); // Send command string
00100     nack    |= i2c.read( addr, &cmd, 1); // Send command string
00101     
00102     if ( nack )
00103         iic_error();        
00104     
00105     return ( cmd );
00106 }
00107 
00108 
00109 short iic_read_short( char addr, char reg )
00110 {
00111     char cmd[ 2 ];
00112     int nack;
00113 
00114     cmd[ 0 ]    = reg;
00115    
00116     nack     = i2c.write( addr, cmd, 1); // Send command string
00117     nack    |= i2c.read( addr, cmd, 2); // Send command string
00118     
00119     if ( nack )
00120         iic_error();        
00121 
00122     return ( ((short)cmd[ 0 ]) << 8 | cmd[ 1 ] );
00123 }
00124 
00125 
00126 void iic_error( void )
00127 {
00128     pc.printf( "I2C error\n" );
00129 
00130     for ( int i = 0; i < 4; i++ )
00131         led[ i ]    = i & 0x01;
00132     
00133     wait ( 0.2 );
00134     
00135     for ( int i = 0; i < 4; i++ )
00136         led[ i ]    = !(i & 0x01);
00137         
00138     wait ( 0.2 );
00139 }
00140