From the mbed microcontroller Handbook.

BusIn

/media/uploads/mbedofficial/digitalin_interfaces.png

The BusIn interface is used to create a number of DigitalIn pins that can be read as one value.

Any of the numbered mbed pins can be used as a DigitalIn in the BusIn.

Hello World!

Control all the LEDs as a single value

#include "mbed.h"

BusIn nibble(p5, p6, p18, p11);

int main() {
    while(1) {
        switch(nibble) {
            case 0x3: printf("Hello!\n"); break; // p5 and p6 are 1
            case 0x8: printf("World!\n"); break; // p11 is 1
        }
    }
}

API

API summary

BusIn	A digital input bus, used for reading the state of a collection of pins
Configuration Methods
BusIn	Create an BusIn, connected to the specified pins
Access Methods
read	Read the value of the input bus
Access Method Shorthand
operator int()	A shorthand for read

class BusIn : public Base

A digital input bus, used for reading the state of a collection of pins

BusIn( PinName p0,
PinName p1 = NC,
PinName p2 = NC,
PinName p3 = NC,
PinName p4 = NC,
PinName p5 = NC,
PinName p6 = NC,
PinName p7 = NC,
PinName p8 = NC,
PinName p9 = NC,
PinName p10 = NC,
PinName p11 = NC,
PinName p12 = NC,
PinName p13 = NC,
PinName p14 = NC,
PinName p15 = NC,
const char * name = NULL )

Create an BusIn, connected to the specified pins