File content as of revision 0:09c1e7c28d04:

 /*Program Example 7.6: I2C Slave, when called transfers switch state to mbed acting as
Master, and displays state of Master’s switches on its leds.
*/
#include <mbed.h>
I2CSlave slave(p9, p10); //Configure I2C slave
DigitalOut red_led(p25); //red led
DigitalOut green_led(p26); //green led
DigitalIn switch_ip1(p5);
DigitalIn switch_ip2(p6);

char switch_word ; //word we will send
char recd_val; //value received from master

int main() 
{
    slave.address(0x52);
    while (1) {
        //set up switch_word from switches that are pressed
        switch_word=0xa0; //set up a recognizable output pattern
        if (switch_ip1==1)
            switch_word=switch_word | 0x01;
        if (switch_ip2==1)
            switch_word=switch_word | 0x02;
        slave.write(switch_word); //load up word to send
        //test for I2C, and act accordingly
        int i = slave.receive();
        if (i == 3)
            { 
            //slave is addressed, Master will write
            recd_val= slave.read();
            //now set leds according to received word
            red_led=0; //preset both to 0
            green_led=0;
            recd_val=recd_val & 0x03; //AND out unwanted bits
            if (recd_val==1)
                red_led=1;
            if (recd_val==2)
                green_led=1;    
            if (recd_val==3)
                {
                red_led=1;
                green_led=1;
                }
            }
        }
}