import smbus
import time

#bus = smbus.SMBus(0) # Rev 1 Pi
bus = smbus.SMBus(1) # Rev 2 Pi

DEVICE = 0x20 # Device Adresse (A0-A2)
IODIRA = 0x00 # Pin Register fuer die Richtung
IODIRB = 0x01 # Pin Register fuer die Richtung
OLATB = 0x15 # Register fuer Ausgabe (GPB)
GPIOA = 0x12 # Register fuer Eingabe (GPA)

# Define GPA pin 7 as input (10000000 = 0x80)
# Binary: 0 means output, 1 means input
bus.write_byte_data(DEVICE,IODIRA,0x80)

# Define all GPB pins as output (00000000 = 0x00)
bus.write_byte_data(DEVICE,IODIRB,0x00)

# Set all 7 output bits to 0
bus.write_byte_data(DEVICE,OLATB,0)

# Function that makes all LEDs light up.
def aufleuchten():
	for MyData in range(1,8):
		# Count from 1 to 8, which is binary
		# from 001 to 111.
		bus.write_byte_data(DEVICE,OLATB,MyData)
		print "Zahl:", MyData, "Binaer:", '{0:08b}'.format(MyData)
		time.sleep(1)
		# Reset all pins to 0 again
		bus.write_byte_data(DEVICE,OLATB,0)

# Endless loop waiting at the push of a button
while True:
	# Read status of GPIOA register
	Taster = bus.read_byte_data(DEVICE,GPIOA)

	if Taster & 0b10000000 == 0b10000000:
		print "Taster gedrueckt"
		aufleuchten()