diff --git a/Code/C_Code/20.1.1_I2CLCD1602/I2CLCD1602.c b/Code/C_Code/20.1.1_I2CLCD1602/I2CLCD1602.c
index cbab64b..ebbc582 100644
--- a/Code/C_Code/20.1.1_I2CLCD1602/I2CLCD1602.c
+++ b/Code/C_Code/20.1.1_I2CLCD1602/I2CLCD1602.c
@@ -2,7 +2,7 @@
 * Filename    : I2CLCD1602.c
 * Description : Use the LCD display data
 * Author      : freenove
-* modification: 2016/06/25
+* modification: 2017/04/18
 **********************************************************************/
 #include <stdlib.h>
 #include <stdio.h>
@@ -11,7 +11,8 @@
 #include <lcd.h>
 #include <time.h>
 
-#define pcf8574_address 0x27        // default I2C address of Pcf8574
+//#define pcf8574_address 0x27        // default I2C address of Pcf8574
+#define pcf8574_address 0x3F        // default I2C address of Pcf8574A
 #define BASE 64         // BASE is not less than 64
 //////// Define the output pins of the PCF8574, which are directly connected to the LCD1602 pin.
 #define RS      BASE+0
diff --git a/Code/Python_Code/20.1.1_I2CLCD1602/I2CLCD1602.py b/Code/Python_Code/20.1.1_I2CLCD1602/I2CLCD1602.py
index e9e78e0..eb48bda 100644
--- a/Code/Python_Code/20.1.1_I2CLCD1602/I2CLCD1602.py
+++ b/Code/Python_Code/20.1.1_I2CLCD1602/I2CLCD1602.py
@@ -3,7 +3,7 @@
 # Filename    : I2CLCD1602.py
 # Description : Use the LCD display data
 # Author      : freenove
-# modification: 2016/06/26
+# modification: 2017/04/18
 ########################################################################
 from PCF8574 import PCF8574_GPIO
 from Adafruit_LCD1602 import Adafruit_CharLCD
@@ -33,9 +33,17 @@ def loop():
 def destroy():
     lcd.clear()
     
-address = 0x27  # I2C address of the PCF8574 chip.
+PCF8574_address = 0x27  # I2C address of the PCF8574 chip.
+PCF8574A_address = 0x3F  # I2C address of the PCF8574A chip.
 # Create PCF8574 GPIO adapter.
-mcp = PCF8574_GPIO(address)
+try:
+	mcp = PCF8574_GPIO(PCF8574_address)
+except:
+	try:
+		mcp = PCF8574_GPIO(PCF8574A_address)
+	except:
+		print 'I2C Address Error !'
+		exit(1)
 # Create LCD, passing in MCP GPIO adapter.
 lcd = Adafruit_CharLCD(pin_rs=0, pin_e=2, pins_db=[4,5,6,7], GPIO=mcp)
 
diff --git a/Code/Python_Code/20.1.1_I2CLCD1602/PCF8574.py b/Code/Python_Code/20.1.1_I2CLCD1602/PCF8574.py
index 9206f4a..50fb5ce 100644
--- a/Code/Python_Code/20.1.1_I2CLCD1602/PCF8574.py
+++ b/Code/Python_Code/20.1.1_I2CLCD1602/PCF8574.py
@@ -2,7 +2,7 @@
 # Filename    : PCF8574.py
 # Description : PCF8574 as Raspberry GPIO
 # Author      : freenove
-# modification: 2016/06/26
+# modification: 2017/04/18
 ########################################################################
 import smbus
 import time
@@ -15,6 +15,7 @@ class PCF8574_I2C(object):
 		self.bus = smbus.SMBus(1)
 		self.address = address
 		self.currentValue = 0
+		self.writeByte(0)	#I2C test.
 		
 	def readByte(self):#Read PCF8574 all port of the data
 		#value = self.bus.read_byte(self.address)
diff --git a/Tutorial.pdf b/Tutorial.pdf
index cd4581c..4d37c71 100644
Binary files a/Tutorial.pdf and b/Tutorial.pdf differ