main2.py

# high chip select means writing, low means reading
# clock is negative edged
import RPi.GPIO as GPIO
from time import time

GPIO.setmode(GPIO.BCM)

data_pins = [24, 4, 17, 22, 13, 25, 18, 23]
clock_pin = 16
chip_select = 26


GPIO.setup(clock_pin, GPIO.OUT)
GPIO.setup(chip_select, GPIO.OUT)


def send_byte(byte_out):
    """
    Send a single byte.
    """
    GPIO.output(clock_pin, 0)
    # set the chip select to write
    GPIO.output(chip_select, 1)
    # send the byte 
    values = [(ord(byte_out) >> i) % 2 for i in range(0, 8)]
    GPIO.setup(data_pins, GPIO.OUT)
    GPIO.output(data_pins, values)
    # flash the clock pin
    GPIO.output(clock_pin, 1)
    GPIO.output(clock_pin, 0)   


def get_byte():
    """
    Get a single byte.
    """
    GPIO.setup(data_pins, GPIO.IN)
    # read the data pins
    GPIO.output(chip_select, 0)
    GPIO.output(clock_pin, 1)
    GPIO.output(clock_pin, 0)
    value = 0
    for i in range(0, 8):
        value += GPIO.input(data_pins[i]) << i
    return value


def read_dimension(dimension):
    # first, set the dimension (x, y, z)
    send_byte(dimension)
    first_byte = get_byte()
    second_byte = get_byte()
    return first_byte + (second_byte << 8)


if __name__ == "__main__":
    while True:
        start = time()
        x_val = read_dimension(b'x')
        y_val = read_dimension(b'y')
        z_val = read_dimension(b'z')
        print(x_val, y_val, z_val, time()-start)