[Advanced I/O]
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 (taken high, then low) to indicate that the bit is available.
Note: if you’re interfacing with a device that’s clocked by rising edges, you’ll need to make sure that the clock pin is low before the call to shiftOut()
, e.g. with a call to digitalWrite(clockPin, LOW)
.
This is a software implementation; see also the SPI library, which provides a hardware implementation that is faster but works only on specific pins.
Syntax
shiftOut(dataPin, clockPin, bitOrder, value)
Parameters
dataPin
: the pin on which to output each bit (int)clockPin
: the pin to toggle once thedataPin
has been set to the correct value (int)bitOrder
: which order to shift out the bits; eitherMSBFIRST
orLSBFIRST
. (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(dataPin, 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 Code
For accompanying circuit, refer to the Arduino 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
Language Reference Home
The text of the 86Duino reference is a modification of the Arduino reference and is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.