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BusIn class hierarchy

With the BusIn API, you can combine a number of DigitalIn pins to read them at once. This abstraction is useful for checking multiple inputs together as single interface instead of individual pins.

You can use any of the numbered Arm Mbed pins as a DigitalIn in the BusIn.


  • You can have up to 16 pins in a Bus.
  • The order of pins in the constructor is the reverse order of the pins in the byte order. If you have BusIn(a,b,c,d,e,f,g,h) then the order of bits in the byte would be hgfedcba with a being bit 0, b being bit 1, c being bit 2 and so on.

BusIn class reference

Public Member Functions
 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)
 Create an BusIn, connected to the specified pins. More...
 BusIn (PinName pins[16])
 Create an BusIn, connected to the specified pins. More...
int read ()
 Read the value of the input bus. More...
void mode (PinMode pull)
 Set the input pin mode. More...
int mask ()
 Binary mask of bus pins connected to actual pins (not NC pins) If bus pin is in NC state make corresponding bit will be cleared (set to 0), else bit will be set to 1. More...
 operator int ()
 A shorthand for read() More...
DigitalInoperator[] (int index)
 Access to particular bit in random-iterator fashion. More...

BusIn hello, world

 * Copyright (c) 2014-2020 Arm Limited and affiliates.
 * SPDX-License-Identifier: Apache-2.0

#include "mbed.h"

BusIn nibble(D0, D1, D2, D3); // Change these pins to buttons on your board.

int main()

    // Optional: set mode as PullUp/PullDown/PullNone/OpenDrain

    while (1) {
        // check bits set in nibble
        switch (nibble & nibble.mask()) { // read the bus and mask out bits not being used
            case 0x0:
                printf("0b0000, D3,D2,D1,D0 are low  \n\r");
            case 0x1:
                printf("0b0001,          D0  is high \n\r");
            case 0x2:
                printf("0b0010,       D1     is high \n\r");
            case 0x3:
                printf("0b0011,       D1,D0 are high \n\r");
            case 0x4:
                printf("0b0100,    D2        is high \n\r");
            case 0x5:
                printf("0b0101,    D2,  ,D0 are high \n\r");
            case 0x6:
                printf("0b0110,    D2,D1    are high \n\r");
            case 0x7:
                printf("0b0111,    D2,D1,D0 are high \n\r");
            case 0x8:
                printf("0b1000, D3           is high \n\r");
            // ...
            case 0xF:
                printf("0b1111, D3,D2,D1,D0 are high \n\r");

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