--- /dev/null
+#include <avr/io.h>
+#define F_CPU 1000000UL //1MHz default internal RC oscillator setting
+//util/delay.h and util/setbaud.h
+
+#define USART_BAUDRATE 9600
+#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)
+
+int main (void)
+{
+ char ReceivedByte;
+
+ UCSRB |= (1 << RXEN) | (1 << TXEN); // Turn on the transmission and reception circuitry
+ //UCSRC |= (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1); // Use 8-bit character sizes (not in attiny2313?)
+
+ UBRRH = (BAUD_PRESCALE >> 8); // Load upper 8-bits of the baud rate value into the high byte of the UBRR register
+ UBRRL = BAUD_PRESCALE; // Load lower 8-bits of the baud rate value into the low byte of the UBRR register
+
+ for (;;) // Loop forever
+ {
+ while ((UCSRA & (1 << RXC)) == 0) {}; // Do nothing until data have been received and is ready to be read from UDR
+ ReceivedByte = UDR; // Fetch the received byte value into the variable "ByteReceived"
+
+ while ((UCSRA & (1 << UDRE)) == 0) {}; // Do nothing until UDR is ready for more data to be written to it
+ UDR = ReceivedByte; // Echo back the received byte back to the computer
+ }
+}
+