diff --git a/yaMBSiavr.c b/yaMBSiavr.c
index a62ae16..9422034 100644
--- a/yaMBSiavr.c
+++ b/yaMBSiavr.c
@@ -214,12 +214,15 @@ ISR(UART_TRANSMIT_COMPLETE_INTERRUPT)
 
 void modbusInit(void)
 {
-	UBRRH = (unsigned char)(Baud>>8);
-	UBRRL = (unsigned char)Baud;
-	UART_CONTROL = (1<<RXCIE)|(1<<RXEN)|(1<<TXEN); // USART receiver and transmitter and receive complete interrupt
-	UART_STATUS |= (1<<U2X); //double speed mode. 
-	UCSRC = (3<<UCSZ0); //Frame Size
-	UART_CONTROL|=(1<<TXCIE); //Transmit Complete Interrupt an
+	UBRRH = (unsigned char)(UBRR>>8);
+	UBRRL = (unsigned char)UBRR;
+	UART_STATUS = (1<<U2X); //double speed mode.
+#ifdef URSEL   // if UBRRH and UCSRC share the same I/O location , e.g. ATmega8
+	UCSRC = (1<<URSEL)|(3<<UCSZ0); //Frame Size
+#else
+   UCSRC = (3<<UCSZ0); //Frame Size
+#endif
+	UART_CONTROL = (1<<TXCIE)|(1<<RXCIE)|(1<<RXEN)|(1<<TXEN); // USART receiver and transmitter and receive complete interrupt
 	#if PHYSICAL_TYPE == 485
 	TRANSCEIVER_ENABLE_PORT_DDR|=(1<<TRANSCEIVER_ENABLE_PIN);
 	transceiver_rxen();
diff --git a/yaMBSiavr.h b/yaMBSiavr.h
index 3a2b094..9c92321 100644
--- a/yaMBSiavr.h
+++ b/yaMBSiavr.h
@@ -51,6 +51,9 @@ THE POSSIBILITY OF SUCH DAMAGE.
  *  @author Max Brueggemann www.maxbrueggemann.de
  */
 
+/* define baudrate of modbus */
+#define BAUD 38400L 
+
 /*
 * Definitions for transceiver enable pin.
 */
@@ -72,11 +75,6 @@ THE POSSIBILITY OF SUCH DAMAGE.
 #define UART_CONTROL  UCSRB
 #define UART_DATA     UDR
 #define UART_UDRIE    UDRIE
-/*
- * Change this value if you are using a different frequency and/or
- * different baudrate.
-*/
-#define Baud 25 //38400@16e6Hz
 
 #elif defined(__AVR_ATmega164P__)
 #define UART_TRANSMIT_COMPLETE_INTERRUPT USART1_TX_vect
@@ -95,11 +93,6 @@ THE POSSIBILITY OF SUCH DAMAGE.
 #define U2X U2X1
 #define UBRRH UBRR1H
 #define UBRRL UBRR1L
-/*
- * Change this value if you are using a different frequency and/or
- * different baudrate.
-*/
-#define Baud 64 //38400@20e6Hz
 
 #elif defined(__AVR_ATmega168PA__)|(__AVR_ATmega88PA__)|(__AVR_ATmega328PA__)
 #define UART_TRANSMIT_COMPLETE_INTERRUPT USART_TX_vect
@@ -141,11 +134,6 @@ THE POSSIBILITY OF SUCH DAMAGE.
 #define U2X U2X0
 #define UBRRH UBRR0H
 #define UBRRL UBRR0L
-/*
- * Change this value if you are using a different frequency and/or
- * different baudrate.
-*/
-#define Baud 64 //38400@20e6Hz
 
 #elif defined(__AVR_ATmega8__)|| defined(__AVR_ATmega16__) || defined(__AVR_ATmega32__) || defined(__AVR_ATmega323__)
 #define UART_TRANSMIT_COMPLETE_INTERRUPT USART_TXC_vect
@@ -156,17 +144,15 @@ THE POSSIBILITY OF SUCH DAMAGE.
 #define UART_DATA     UDR
 #define UART_UDRIE    UDRIE
 
-/*
- * Change this value if you are using a different frequency and/or
- * different baudrate.
-*/
-#define Baud 25 //38400@8e6Hz double speed mode
-
-
 #else
 #error "no definition available"
 #endif
 
+#ifndef F_CPU
+#error " F_CPU not defined "
+#else
+   #define UBRR (F_CPU / 8 / BAUD ) -1 
+#endif /* F_CPU */
 /*
  * Available address modes.
 */
@@ -345,3 +331,4 @@ extern uint8_t modbusExchangeBits(volatile uint8_t *ptrToInArray, uint16_t start
 *
 */
 extern uint8_t modbusExchangeRegisters(volatile uint16_t *ptrToInArray, uint16_t startAddress, uint16_t size);
+