// Define Connections to 74HC165
#define S1_CLOCK_ENABLE_CE  A3
#define S1_DATA_IN_Q7       A2
#define S1_LOAD_PL          A1
#define S1_CLOCK_IN_CP      A0
 
#define S2_CLOCK_ENABLE_CE  A7
#define S2_DATA_IN_Q7       A6
#define S2_LOAD_PL          A5
#define S2_CLOCK_IN_CP      A4

void setup()
{
  // Setup Serial Monitor
  Serial.begin(115200);
 
  // Setup 74HC165 connections
  pinMode(S1_CLOCK_ENABLE_CE, OUTPUT);
  pinMode(S1_DATA_IN_Q7, INPUT);
  pinMode(S1_LOAD_PL, OUTPUT);
  pinMode(S1_CLOCK_IN_CP, OUTPUT);

  pinMode(S2_CLOCK_ENABLE_CE, OUTPUT);
  pinMode(S2_DATA_IN_Q7, INPUT);
  pinMode(S2_LOAD_PL, OUTPUT);
  pinMode(S2_CLOCK_IN_CP, OUTPUT);
}

void printBin(byte data) {
  for (int i = 0; i < 8; i++) {
    Serial.print((data >> i) & 0x01);
  }
  Serial.println();
}

void readShiftRegister(
  const char *shift_name,
  int8_t CLOCK_ENABLE_CE, 
  int8_t DATA_IN_Q7, 
  int8_t LOAD_PL, 
  int8_t CLOCK_IN_CP
){
  // Write pulse to load pin
  digitalWrite(LOAD_PL, LOW);
  delayMicroseconds(5);
  digitalWrite(LOAD_PL, HIGH);
  delayMicroseconds(5);
 
  // Get data from 74HC165
  digitalWrite(CLOCK_IN_CP, HIGH);
  digitalWrite(CLOCK_ENABLE_CE, LOW);
  byte incoming = shiftIn(DATA_IN_Q7, CLOCK_IN_CP, MSBFIRST);
  digitalWrite(CLOCK_ENABLE_CE, HIGH);
 
  // Print to serial monitor
  Serial.print(shift_name);
  Serial.print(" - Pin States:\n");
  printBin(incoming);
}

void loop()
{
  readShiftRegister(
    "original",
    S1_CLOCK_ENABLE_CE,
    S1_DATA_IN_Q7,
    S1_LOAD_PL,
    S1_CLOCK_IN_CP
  );
  readShiftRegister(
    "emulated",
    S2_CLOCK_ENABLE_CE,
    S2_DATA_IN_Q7,
    S2_LOAD_PL,
    S2_CLOCK_IN_CP
  );

  delay(500);
}