diff --git a/B15F.elf b/B15F.elf
index d842f33..3ecadd1 100644
Binary files a/B15F.elf and b/B15F.elf differ
diff --git a/B15F.hex b/B15F.hex
index 3c9bc2c..54d07c1 100644
--- a/B15F.hex
+++ b/B15F.hex
@@ -6,91 +6,100 @@
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 :00000001FF
diff --git a/Makefile b/Makefile
index c78a78d..bc20456 100644
--- a/Makefile
+++ b/Makefile
@@ -10,9 +10,9 @@ OBJCOPY_PATH = C:\avr8-gnu-toolchain-win32_x86\bin\avr-objcopy.exe
 
 OUTPUT  = B15F.elf
 HEX		= B15F.hex
-CFLAGS  = -std=c++14 -O3 -mmcu=atmega1284 -DF_CPU=20000000 -DPIO_DISABLE_I2C
+CFLAGS  = -std=c++14 -O3 -mmcu=atmega1284 -DF_CPU=20000000
 LDFLAGS = 
-OBJECTS = main.o spi.o mcp23s17.o tlc5615.o adu.o selftest.o global_vars.o
+OBJECTS = main.o spi.o mcp23s17.o tlc5615.o adu.o selftest.o global_vars.o usart.o
 
 
 COMPILE = $(COMPILER_PATH) $(CFLAGS)
diff --git a/global_vars.cpp b/global_vars.cpp
index 154f77a..ac6f544 100644
--- a/global_vars.cpp
+++ b/global_vars.cpp
@@ -7,3 +7,4 @@ MCP23S17 sw(spi, SPIADR::SWITCH);
 TLC5615 dac0(spi, SPIADR::AA0);
 TLC5615 dac1(spi, SPIADR::AA1);
 ADU adu;
+USART usart;
diff --git a/global_vars.h b/global_vars.h
index aff0a83..c7ecd0c 100644
--- a/global_vars.h
+++ b/global_vars.h
@@ -4,6 +4,7 @@
 #include "mcp23s17.h"
 #include "tlc5615.h"
 #include "adu.h"
+#include "usart.h"
 
 extern SPI spi;
 extern MCP23S17 beba0;
@@ -12,5 +13,6 @@ extern MCP23S17 sw;
 extern TLC5615 dac0;
 extern TLC5615 dac1;
 extern ADU adu;
+extern USART usart;
 
 #endif // GLOBAL_VARS_H
diff --git a/main.cpp b/main.cpp
index 56f2c20..1650305 100644
--- a/main.cpp
+++ b/main.cpp
@@ -29,6 +29,15 @@ void initAll()
 	sw.setDirB(0xFF); // alle Eingang
 
 	adu.init();
+	usart.init();
+}
+
+void handleRequest()
+{
+	const uint8_t req = usart.readByte();
+	uint8_t dummy = usart.readByte();
+	usart.writeByte(USART::MSG_OK);
+	usart.writeByte(dummy);
 }
 
 int main()
@@ -43,7 +52,7 @@ int main()
 	
 	while(1)
 	{
-		testAll();
+		handleRequest();
 	}
 
 	return 0;
diff --git a/usart.cpp b/usart.cpp
new file mode 100644
index 0000000..b50c905
--- /dev/null
+++ b/usart.cpp
@@ -0,0 +1,26 @@
+#include "usart.h"
+
+void USART::init()
+{
+	UCSR0B = _BV(RXEN0) | _BV(TXEN0);
+
+	// Einstellen des Datenformats: 8 Datenbits, 1 Stoppbit
+	UCSR0C = _BV(UCSZ00) |_BV(UCSZ01);// (1<<URSEL0)|(1<<UCSZ10)|(1<<UCSZ00);
+
+	// setze Baudrate
+	UBRR0H = (((F_CPU / (16UL * BAUDRATE))-1) >> 8) & 0xFF;
+	UBRR0L =  ((F_CPU / (16UL * BAUDRATE))-1) & 0xFF;
+
+}
+
+void USART::writeByte(uint8_t b)
+{
+	UDR0 = b;
+	while(!(UCSR0A & _BV(TXC0)));
+}
+
+uint8_t USART::readByte()
+{
+	while (!(UCSR0A & (1<<RXC0)));
+    return UDR0;
+}
diff --git a/usart.h b/usart.h
new file mode 100644
index 0000000..39bdee1
--- /dev/null
+++ b/usart.h
@@ -0,0 +1,20 @@
+#ifndef USART_H
+#define USART_H
+
+#include <avr/io.h>
+#include <stdint.h>
+
+constexpr uint16_t BAUDRATE = 38400UL; //9600UL//9600
+
+class USART
+{
+public:
+	void init(void);
+	void writeByte(uint8_t);
+	uint8_t readByte(void);
+
+	constexpr static uint8_t MSG_OK = 0xFF;
+	constexpr static uint8_t MSG_FAIL = 0xFE;
+};
+
+#endif // USART_H