Use Program Example 7.3 on pages 123-124 to answer the following questions: a) explain how the command if(ser_port.receive()) works. b) review the block of code following the command if(ser_port.receive()): will it be true even if no button is closed on the master? Is it necessary to close a button on the master for the slave to send the switch_word variable back to the master?

here is the program

/*Program Example 7.3: Sets the mbed up as Slave, and exchanges data with a Master, sending its own switch positions, and displaying those of the Master. as SPI slave.

*/

#include "mbed.h"

SPISlave ser_port(p11,p12,p13,p14); // mosi, miso, sclk, ssel

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() {

//default formatting applied

while(1) {

//set up switch_word from switches that are pressed

switch_word=0xa0; //set up a recognisable output pattern

if (switch_ip1==1)

switch_word=switch_word|0x01;

if (switch_ip2==1)

switch_word=switch_word|0x02;

if(ser_port.receive()) { //test if data transfer has occurred

recd_val = ser_port.read(); // Read byte from master

ser_port.reply(switch_word); // Make this the next reply

}

//now set leds according to received word

...

(continues as in Program Example 7.2)

...

}

}