Shift Register

From ElectroDragon
Jump to: navigation, search

basic shift

void setup()
{
  pinMode(clock, OUTPUT); // make the clock pin an output
  pinMode(data , OUTPUT); // make the data pin an output
  shiftOut(data, clock, LSBFIRST, B10101010); // send this binary value to the shift register
}

SIPO 74HC595

PISO 74HC165

74hc165 PISO.png
/*
 * SN74HC165N_shift_reg
 *
 * Program to shift in the bit values from a SN74HC165N 8-bit
 * parallel-in/serial-out shift register.
 *
 * This sketch demonstrates reading in 16 digital states from a
 * pair of daisy-chained SN74HC165N shift registers while using
 * only 4 digital pins on the Arduino.
 *
 * You can daisy-chain these chips by connecting the serial-out
 * (Q7 pin) on one shift register to the serial-in (Ds pin) of
 * the other.
 * 
 * Of course you can daisy chain as many as you like while still
 * using only 4 Arduino pins (though you would have to process
 * them 4 at a time into separate unsigned long variables).
 * 
*/
 
/* How many shift register chips are daisy-chained.
*/
#define NUMBER_OF_SHIFT_CHIPS   2
 
/* Width of data (how many ext lines).
*/
#define DATA_WIDTH   NUMBER_OF_SHIFT_CHIPS * 8
 
/* Width of pulse to trigger the shift register to read and latch.
*/
#define PULSE_WIDTH_USEC   5
 
/* Optional delay between shift register reads.
*/
#define POLL_DELAY_MSEC   1
 
/* You will need to change the "int" to "long" If the
 * NUMBER_OF_SHIFT_CHIPS is higher than 2.
*/
#define BYTES_VAL_T unsigned int
 
int ploadPin        = 8;  // Connects to Parallel load pin the 165
int clockEnablePin  = 9;  // Connects to Clock Enable pin the 165
int dataPin         = 11; // Connects to the Q7 pin the 165
int clockPin        = 12; // Connects to the Clock pin the 165
 
BYTES_VAL_T pinValues;
BYTES_VAL_T oldPinValues;
 
/* This function is essentially a "shift-in" routine reading the
 * serial Data from the shift register chips and representing
 * the state of those pins in an unsigned integer (or long).
*/
BYTES_VAL_T read_shift_regs()
{
    long bitVal;
    BYTES_VAL_T bytesVal = 0;
 
    /* Trigger a parallel Load to latch the state of the data lines,
    */
    digitalWrite(clockEnablePin, HIGH);
    digitalWrite(ploadPin, LOW);
    delayMicroseconds(PULSE_WIDTH_USEC);
    digitalWrite(ploadPin, HIGH);
    digitalWrite(clockEnablePin, LOW);
 
    /* Loop to read each bit value from the serial out line
     * of the SN74HC165N.
    */
    for(int i = 0; i < DATA_WIDTH; i++)
    {
        bitVal = digitalRead(dataPin);
 
        /* Set the corresponding bit in bytesVal.
        */
        bytesVal |= (bitVal << ((DATA_WIDTH-1) - i));
 
        /* Pulse the Clock (rising edge shifts the next bit).
        */
        digitalWrite(clockPin, HIGH);
        delayMicroseconds(PULSE_WIDTH_USEC);
        digitalWrite(clockPin, LOW);
    }
 
    return(bytesVal);
}
 
/* Dump the list of zones along with their current status.
*/
void display_pin_values()
{
    Serial.print("Pin States:\r\n");
 
    for(int i = 0; i < DATA_WIDTH; i++)
    {
        Serial.print("  Pin-");
        Serial.print(i);
        Serial.print(": ");
 
        if((pinValues >> i) & 1)
            Serial.print("HIGH");
        else
            Serial.print("LOW");
 
        Serial.print("\r\n");
    }
 
    Serial.print("\r\n");
}
 
void setup()
{
    Serial.begin(9600);
 
    /* Initialize our digital pins...
    */
    pinMode(ploadPin, OUTPUT);
    pinMode(clockEnablePin, OUTPUT);
    pinMode(clockPin, OUTPUT);
    pinMode(dataPin, INPUT);
 
    digitalWrite(clockPin, LOW);
    digitalWrite(ploadPin, HIGH);
 
    /* Read in and display the pin states at startup.
    */
    pinValues = read_shift_regs();
    display_pin_values();
    oldPinValues = pinValues;
}
 
void loop()
{
    /* Read the state of all zones.
    */
    pinValues = read_shift_regs();
 
    /* If there was a chage in state, display which ones changed.
    */
    if(pinValues != oldPinValues)
    {
        Serial.print("*Pin value change detected*\r\n");
        display_pin_values();
        oldPinValues = pinValues;
    }
 
    delay(POLL_DELAY_MSEC);
}

Compare

  • CD4094 - 8-Bit Shift Register/Latch with 3-STATE Outputs
Type Compare Type
74LS164
  • Has AND'd inputs (A and B). Just set one HIGH and use the other.
  • DOES NOT HAVE a Latch.
8-Bit Serial-In, Parallel-Out Shift, SIPO
74HC595
  • Tri-state outputs so they can share a bus with other chips.
8-Bit Serial-In, Parallel-Out Shift, SIPO
74HC165 8-Bit parallel-in, serial out shift register, PISO

Schematic

Documents

arduino 7-segment library