Fig. 1

Arduino 74HC595 Serial Shift Register Interfacing

by Lewis Loflin

Here we look into connecting a 74HC595 8-bit serial shift register with 8-bit latch to an Arduino Microcontroller. Fig. 1 shows the internal configuration.

While Arduino has built in commands for serial output by writing our own we can port the basic program to other platforms such as the Raspberry Pi.

// use just k instead of !k 
// for common cathode displays.
void   byteOut(byte j)   {
  byte k;
  for(int i=0; i < 8; i++)   {
    k = j & 0x01;
    digitalWrite(DATA, k); 
    digitalWrite(CLK, HIGH);
    digitalWrite(CLK, LOW); 
    j = j >> 1;
  }
  // latch byte
  digitalWrite(LATCH, HIGH);
  digitalWrite(LATCH, LOW);
}

Above is our serial shift subroutine byteOut(). It's nothing more than a for loop, a bitwise AND, and right-shift that sets or clears the DATA pin, pulses (HIGH then LOW) the shift clock, then after doing that 8 times pulses (HIGH then LOW) the latch pin. Here we shift out the least significant bit first.

Fig. 2

Fig. 2 shows the LED connections. The LED pattern is simply a reproduction of the binary pattern shifted into the 8-bit register. In this case we simply count in binary from 0-255 right to left.

// Count 0-255 74HC595

#define DATA 8 // 74HC595 pin 14
#define LATCH 9 // 74HC595 pin 12
#define CLK 10 // 74HC595 pin 11


void setup()   {
  pinMode(DATA, OUTPUT);  
  pinMode(LATCH, OUTPUT);
  pinMode(CLK, OUTPUT);
  digitalWrite(DATA, 0); 
  digitalWrite(LATCH, 0);
  digitalWrite(CLK, 0);
} // end setup

void loop()   {
  for(int i=0; i<=255; i++)   {
    byteOut(i);
    delay(200);
  }

} //end loop

// use just k instead of !k 
// for common cathode displays.
void   byteOut(byte j)   {
  byte k;
  for(int i=0; i < 8; i++)   {
    k = j & 0x01;
    digitalWrite(DATA, k); 
    pulseCLK();
    j = j >> 1;
  }
  pulseCS(); // latch byte
}


void pulseCLK()   {
  digitalWrite(CLK, HIGH);
  digitalWrite(CLK, LOW); 
}

void pulseCS()   {
  digitalWrite(LATCH, HIGH);
  digitalWrite(LATCH, LOW);
}