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.. _arduino-shiftout:
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 <http://arduino.cc/en/Reference/SPI>`_
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 <http://arduino.cc/en/Reference/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 <http://arduino.cc/en/Tutorial/ShiftOut>`_.*
::
//**************************************************************//
// 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);
}
}
|
