File content as of revision 2:6144709f1700:

/* MCP23S17 - drive the Microchip MCP23S17 16-bit Port Extender using SPI
* Copyright (c) 2010 Romilly Cocking
* Released under the MIT License: http://mbed.org/license/mit
*
* version 0.1
*/
#include "mbed.h"

#ifndef  SER23K256_H
#define  SER23K256_H

// all register addresses assume IOVCON.BANK = 0 (POR default)

#define IODIRA 0x00
#define IODIRB 0x01
#define IOCON  0x0A
#define GPIOA  0x12
#define GPIOB  0x13
#define OLATA  0x14
#define OLATB  0x15

// Control settings

#define IOCON_BANK  0x80 // Banked registers
#define IOCON_BYTE_MODE 0x20 // Disables sequential operation. If bank = 0, operations toggle between A and B registers
#define IOCON_HAEN  0x08 // Hardware address enable

class MCP23S17 {
public:
    MCP23S17(SPI& spi, PinName ncs, char writeOpcode);
    void directionA(char direction);
    void directionB(char direction);
    char inputA();
    char inputB();
    void outputA(char byte);
    void outputB(char byte);
protected:
    SPI& _spi;
    DigitalOut _ncs;
    void _init();
    void _write(char address, char data);
    char _read(char address);
    char _readOpcode;
    char _writeOpcode;
};

#endif