main.cpp

00001 /*Program Example 7.5: I2C Master, transfers switch state to second mbed acting as slave, and displays state of slave's switches on its leds.
00002                                                                               */
00003 #include "mbed.h"
00004 I2C i2c_port(p9, p10);     //Configure a serial port, pins 9 and 10 are sda, scl
00005 DigitalOut red_led(p25);   //red led
00006 DigitalOut green_led(p26); //green led
00007 DigitalIn  switch_ip1(p5); //input switch
00008 DigitalIn  switch_ip2(p6);
00009 
00010 char switch_word ;        //word we will send
00011 char recd_val;            //value received from slave
00012 const int addr = 0x52;    //the I2C slave address, an arbitrary even number
00013 
00014 int main() {
00015   while(1) {
00016     switch_word=0xa0;                    //set up a recognisable output pattern
00017     if (switch_ip1==1)
00018       switch_word=switch_word|0x01;      //OR in lsb
00019     if (switch_ip2==1)
00020       switch_word=switch_word|0x02;      //OR in next lsb
00021     //send a single byte of data, in correct I2C package
00022     i2c_port.start();                    //force a start condition
00023     i2c_port.write(addr);                //send the address
00024     i2c_port.write(switch_word);         //send one byte of data, ie switch_word
00025     i2c_port.stop();                     //force a stop condition
00026     wait(0.002);       
00027     //receive a single byte of data, in correct I2C package
00028     i2c_port.start();
00029     i2c_port.write(addr|0x01);          //send address, with R/W bit set to Read
00030     recd_val=i2c_port.read(addr);       //Read and save the received byte
00031     i2c_port.stop();                    //force a stop condition
00032 
00033     //set leds according to incoming word from slave
00034     red_led=0;              //preset both to 0
00035     green_led=0; 
00036     recd_val=recd_val&0x03; //AND out unwanted bits
00037     if (recd_val==1)
00038       red_led=1;
00039     if (recd_val==2)
00040       green_led=1;
00041     if (recd_val==3){
00042       red_led=1;
00043       green_led=1;
00044     }
00045   }
00046 }