1. Chap.6.3 UART

2. UART Universal Asynchronous Receiver/Transmitter USART
a piece of computer hardware that translates data between parallel and serial forms
parallel : inside computer
serial : serial communication
USART
universal synchronous/asynchronous receiver/transmitter
RS-232C protocol
Baud Rate or bps : bits per second
stop bit : 1, 1.5, 2 bit
parity : error detecting code
data length : number of data bits in a frame

3. USART in ATmega128 – Block Diagram
: Register
: Pin-Out

4. USART in ATmega128 Frame Formats : 1 start bit 5,6,7,8 or 9 data bits
no, even or odd parity bit
1 or 2 stop bits

5. USART in ATmega128
Dual USART
USART0
USART1

6. USART Register
1 data register, 3 control registers, 2 baud rate registers
UDRn - USARTn I/O Data Register (n=0 or 1)
C programming (if USART0 is used)
when transmit, UDR0 = data;
when received, data = UDR0;

7. UCSRnA :USART Control and Status Register A
RXCn : USART Receive Complete
set (=‘1’) when there are unread data in the receive buffer
TXCn: USART Transmit Complete
UDREn: USART Data Register Empty
set (=‘1’) when the buffer is empty and therefore ready to be written
FEn: Frame Error
DORn: Data OverRun
UPEn: Parity Error
U2Xn: Double the USART Transmission Speed
MPCMn: Multi-Processor Communication Mode

8. UCSRnB :USARTn Control and Status Register B
RXCIEn: RX Complete Interrupt Enable
TXCIEn: TX Complete Interrupt Enable
UDRIEn: USART Data Register Empty Interrupt Enable
RXENn: Receiver Enable
set(=‘1’) then receiver is enabled
TXENn: Transmitter Enable
set(=‘1’) then transmitter is enabled
UCSZn2: Character Size
sets the number of data bits combined with UCSZn1:0 bit in UCSRnC
RXB8n: Receive Data Bit 8
TXB8n: Transmit Data Bit 8

9. UCSRnC :USARTn Control and Status Register C
UMSELn: USART Mode Select
asynchronous (=‘0’), synchronous (=‘1’)
UPMn1:0: Parity Mode
USBSn: Stop Bit Select
1 stop bit (=‘0’), 2 stop bits (=‘1’)
UCPOLn: Clock Polarity

10. UCSRnC :USARTn Control and Status Register C
UCSZn1:0: Character Size
UCSZn2: Character Size (in UCSRnB )

11. UBRRnL /UBRRnH - USART Baud Rate Registers
UBRRn[11:0]: USARTn Baud Rate Register
% fosc = system clock freq.

12. Register Addresses and Pin-Out for USART
Address/Pin-Out
USART1
UDR0
UDR1
UCSR0A
UCSR1A
UCSR0B
UCSR1B
UCSR0C
UCSR1C
UBRR0L
UBRR1L
UBRR0H
UBRR1H
RXD0
RXD1
TXD0
TXD1
XCK0
XCK1

13. USART Demo Program
USART 통신
하이퍼 터미널
Demo program
Key Board

14. USART 초기화 Port 설정 USART1 사용 DDRD의 3 bit 는 출력/2 bit 는 입력)
Baud Rate = (fosc = MHz)
No parity
UPM1[1:0 ]= 0 0
1 Stop bit
USBS1 = 0
8 data bits
UCSZ1[2:0] = 0 1 1

15. USART 초기화 - Register Setting
bit 7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
DDRD
UCSR1A
UCSR1B
UCSR1C
UBRR1H
UBRR1L

16. USART 초기화 program
DDRD &= 0xFB; DDRD |= 0x08; UCSR1A = 0x00; UCSR1B = 0x18; UCSR1C = 0x06; UBRR1H = 0x00; UBRR1L = 0x03;

17. Transmit / Receive function
void txd_char(unsigned char data){ while( (UCSR1A & 0x20) == 0 ); UDR1 = data; } unsigned char rxd_char(){ unsigned char data; while( (UCSR1A & 0x80) == 0 ); data = UDR1; return data;

18. USART demo program
#include <avr/io.h> /* txd_char(), rxd_char()의 선언 및 정의 */ int main() { unsigned char text[]=“\r\n Micro-computer USART 1 Demo \r\n”; unsigned char echo[]=“ECHO>>”; unsigned char i=0; /* 초기화 code */ while(text[i] != ‘\0’) txd_char(text[i++]); i = 0; while(echo[i] != ‘\0’) txd_char(echo[i++]); while(1) txd_char(rxd_char()); return 0; }

19. USART demo program 실행 방법
프로그램 컴파일 & 다운로드
ISP Program 창 닫기
AVR-ISP 스위치를 UART로 변경
하이퍼터미널 실행 및 설정
시작 -> 프로그램 -> 보조프로그램 -> 통신 -> 하이퍼터미널

20. 실습 과제 #1. USART0를 이용하여 demo program을 작성하시오.
#2. #include <avr/io.h>를 제거하시오.
#3. 다음의 기능을 수행하는 program을 작성하시오.
‘r’ key : LED off;
‘i’ key : LED 증가 /* 00 -> 01 -> 10 -> 11 -> 00 … */
‘d’ key : LED 감소 /* 00 -> 11 -> 10 -> 01 -> 00 -> 11 … */
‘s’ key : LED on;

21. Reference Code /* Register 정의 */ /* txd_char(), rxd_char()의 선언 및 정의 */
int main() {
/* 변수 선언 */
/* 초기화 code */
while(1) {
cmd = rxd_char();
switch (cmd){
/* key 입력에 따른 작업 수행 */ }
return 0;