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With the BusIn API, you can create a number of DigitalIn pins that you can read as one value. This abstraction is useful for checking multiple inputs at once. You can use this API to write clearer code faster.

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 BusOut(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)
 BusIn (PinName pins[16])
int read ()
void mode (PinMode pull)
int mask ()
 operator int ()
DigitalInoperator[] (int index)
Protected Attributes
DigitalIn_pin [16]
int _nc_mask
PlatformMutex _mutex

BusIn Hello World!

/* mbed Example Program
 * Copyright (c) 2006-2014 ARM Limited
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *     http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.

#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");break;
            case 0x1: printf("0b0001,          D0  is high \n\r");break;
            case 0x2: printf("0b0010,       D1     is high \n\r");break; 
            case 0x3: printf("0b0011,       D1,D0 are high \n\r");break;
            case 0x4: printf("0b0100,    D2        is high \n\r");break;
            case 0x5: printf("0b0101,    D2,  ,D0 are high \n\r");break;
            case 0x6: printf("0b0110,    D2,D1    are high \n\r");break;
            case 0x7: printf("0b0111,    D2,D1,D0 are high \n\r");break;
            case 0x8: printf("0b1000, D3           is high \n\r");break; 
            // ...
            case 0xF: printf("0b1111, D3,D2,D1,D0 are high \n\r");break;
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