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## shiftOut()

#### Description

Shifts out a byte of data one bit at a time. Starts from either the most (i.e. the leftmost) or least (rightmost) significant bit. Each bit is written in turn to a data pin, after which a clock pin is pulsed to indicate that the bit is available.

This is a software implementation; Arduino (as of 0019) also provides an SPI library that uses the hardware implementation.

#### Syntax

shiftOut(dataPin, clockPin, bitOrder, value)

#### Parameters

dataPin: the pin on which to output each bit (int)

clockPin: the pin to toggle once the dataPin has been set to the correct value (int)

bitOrder: which order to shift out the bits; either MSBFIRST or LSBFIRST.
(Most Significant Bit First, or, Least Significant Bit First)

value: the data to shift out. (byte)

#### Returns

None

#### Note

The dataPin and clockPin must already be configured as outputs by a call to pinMode().

shiftOut is currently written to output 1 byte (8 bits) so it requires a two step operation to output values larger than 255.

    // Do this for MSBFIRST serial
    int data = 500;
    // shift out highbyte
    shiftOut(dataPin, clock, MSBFIRST, (data >> 8));
    // shift out lowbyte
    shiftOut(data, clock, MSBFIRST, data);

    // Or do this for LSBFIRST serial
    data = 500;
    // shift out lowbyte
    shiftOut(dataPin, clock, LSBFIRST, data);
    // shift out highbyte
    shiftOut(dataPin, clock, LSBFIRST, (data >> 8));

#### Example

For accompanying circuit, see the tutorial on controlling a 74HC595 shift register.

    //**************************************************************//
    //  Name    : shiftOutCode, Hello World                         //
    //  Author  : Carlyn Maw,Tom Igoe                               //
    //  Date    : 25 Oct, 2006                                      //
    //  Version : 1.0                                               //
    //  Notes   : Code for using a 74HC595 Shift Register           //
    //          : to count from 0 to 255                            //
    //****************************************************************

    //Pin connected to ST_CP of 74HC595
    int latchPin = 8;
    //Pin connected to SH_CP of 74HC595
    int clockPin = 12;
    ////Pin connected to DS of 74HC595
    int dataPin = 11;

    void setup() {
      //set pins to output because they are addressed in the main loop
      pinMode(latchPin, OUTPUT);
      pinMode(clockPin, OUTPUT);
      pinMode(dataPin, OUTPUT);
    }

    void loop() {
      //count up routine
      for (int j = 0; j < 256; j++) {
        //ground latchPin and hold low for as long as you are transmitting
        digitalWrite(latchPin, LOW);
        shiftOut(dataPin, clockPin, LSBFIRST, j);
        //return the latch pin high to signal chip that it
        //no longer needs to listen for information
        digitalWrite(latchPin, HIGH);
        delay(1000);
      }
    }

#### See also

- shiftIn()
- SPI

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