File content as of revision 3:fdb89f47357f:

#include "mbed.h"
#include "MCP23S17.h"
// Create SPI bus
SPI spi(p5, p6, p7);

// Wiring Connections:
// mbed p5,p6,p7 are tied to MCP23S17 SI, SO, SCK pins
// mbed p20 to MCP23S17 CS
// MCP23S17 reset pin pulled high
// MCP23S17 GPA0 connected to GPB0 for loopback test
// A0, A1, A2 of the MCP23S17  are tied to ground on the breadboard, so the 8-bit address for writes is 0x40
// This is referred to as the opcode in the device datasheet
char Opcode = 0x40;

// Next create a MCP23S17
// mbed p20 is connected to ~chipSelect on the MCP23S17
MCP23S17 chip = MCP23S17(spi, p20, Opcode);

// Optional software reset - mbed p14 to MCP23S17 reset pin
// DigitalOut reset(p14);


int main() {
//  The MCP23S17 reset pin can just be pulled high, since it has a power on reset circuit.
//  The reset pin can be used for a software forced reset by pulling it low with an mbed GPIO pin.
//  But just leave it pulled high for this simple demo code.
//  After a power on reset, both IO ports default to input mode

//  Set all 8 Port A bits to output direction
    chip.direction(PORT_A, 0x00);
//  Set all 8 Port B bits to input direction
    chip.direction(PORT_B, 0xFF);
    
   // chip.interruptEnable(PORT_B, 0xFF);

    uint8_t trigger;
    while (1) {
        //Read in PortB and output it to PortA
        trigger = chip.read(PORT_B);
        chip.write(PORT_A, !trigger);
    }
}