Simple test program to shift out some bits to measure the difference between different Atmel chips and SPI vs. shiftOut()

spi-shiftout-test.ino

// Simple test program to shift out some bits to measure the difference between
// different Atmel chips and SPI vs. shiftOut()

#include <SPI.h>

/* for Feather and Arduino Uno 
#define RCLK_PIN 9 // latching pin for the shift registers to show values at their outputs

#define DATA_PIN MOSI
#define CLK_PIN  SCK
// */

//* for attiny85
#define RCLK_PIN 4 // latching pin for the shift registers to show values at their outputs

#define DATA_PIN 1
#define CLK_PIN  2
// */

// pick one of these
//#define SHIFTMODE
#define SPIMODE

void setup() {

  pinMode(RCLK_PIN, OUTPUT);

#ifdef SHIFTMODE
  pinMode(DATA_PIN, OUTPUT);
  pinMode(CLK_PIN, OUTPUT);

  shiftOut(DATA_PIN, CLK_PIN, LSBFIRST, 0);
#endif

#ifdef SPIMODE
  SPI.begin();
  SPI.beginTransaction(SPISettings(16000000, LSBFIRST, SPI_MODE0));
#endif
}

uint8_t num = 0x00;

void loop() {

  digitalWrite(RCLK_PIN, LOW);

#ifdef SHIFTMODE
  shiftOut(DATA_PIN, CLK_PIN, LSBFIRST, num);
#endif

#ifdef SPIMODE
  SPI.transfer(num);
#endif

  digitalWrite(RCLK_PIN, HIGH);

  num += 1;

  delay(200);
}