ECE 371- Unit 10-Part 1

Introduction to Serial I/O

TWO MAJOR CLASSES OF SERIAL DATA INTERFACES

• ASYNCHRONOUS SERIAL I/O

- USES “FRAMING BITS”

(START BIT AND STOP BIT(S))

WITH EACH CHARACTER

idle

Start bit lsb msb

Parity bit

Stop bit(s)

Data value transmitted is 0 0 1 1 1 0 1 1

Parity bit shown represents even parity option

Asynchronous Serial Data Format

• SYNCHRONOUS SERIAL I/O- USES SINGLE “SYNCH” CHARACTER AT BEGINNNG OF

DATA STREAM

OR

- USES SPECIAL CLOCK SIGNAL TO DEFINE BEGINNING OF EACH NEW CHARACTER

Synch char Data charHeader information

Data char Data charData char

etc

Synchronous Serial Data Transmission Format

OR

Data char Data charData char Data char Data charData char

CLASSES OF SERIAL DATA APPLICATION

• COMPUTER TO PERIPHERAL DEVICE

• COMPUTER TO COMPUTER

Computer System

PeripheralDevice

Serial data

Handshaking Signals

Ground

Half-duplex Serial Data Interface Between Computer and Peripheral Device

Computer System

PeripheralDevice

Serial data

Handshaking Signals

Ground

Full-duplex Serial Data Interface Between Computer and Peripheral Device

Computer(DTE)

ModemTelephone

SystemModem

Computer(DTE)

Serial Data CommunicationBetween Computers, Using Modems

RS-232StandardInterface

RS-232StandardInterface

DCEData Communication Equipment

DTE = Data Terminal Equipment

RS-232 is a Standard Interface between DTE and DCE

Laptop COM1 Port

CPU AsynchronousSerial Interface

Modem Telephone Line

Inside PC

RS-232 Standard Interface

• Defines a 25-bit Connector

• Defines the function of each pin

• Defines EIA RS-232 Logic Levels– Serial Data Physical Representation

• Logic “1”: -25 volts ≤ V1 ≤ -5 volts

• Logic “0”: +5 volts ≤ V0 ≤ +25 volts

TXD

RXD

GND

RTS

CTS

DCD

DSR

DTR

RI

DCE

EIA RS-232 Signals of Interest

DTE

Primary RS-232 Signals

• RxD -- Received Data• TxD --Transmitted Data• RTS – Request to Send• CTS – Clear to Send• DTR – Data Terminal Ready - DTE Ready• DSR – Data Set Ready – DCE Ready• RI – Ring Indicator• DCD – Data Carrier Detect• GND -- Ground

EIA RS-232 Interface

COM Connector on PC

SERIAL COMMUNICATION INTERFACE (SCI) ON THE MC9S12DP256B MICROCONTROLLER

• ASYNCHRONOUS SERIAL I/O

• COMPATIBLE WITH RS232 STANDARD

SCI Data FormatsSee p. 211, text, for def.

Serial Data Format

• Idle (no data being transmitted) = “1”

• Start = “0”

• Stop =“1”

• Each data bit is T seconds in length

• Baud = 1/T

• Least Significant Bit Sent First

• Most Significant Bit Sent Last

ASCII Code for Letter A = 0b01000001 = 0x41ASCII Code for Letter B = 0b01000010 = 0x42 ASCII Code for Digit 1 = 0b00110001 = 0x31

Idle Start LSB MSB Stop

A = 1 1 1 0 1 0 0 0 0 0 1 0 1 1B = 1 1 1 0 0 1 0 0 0 0 1 0 1 11 = 1 1 1 0 1 0 0 0 1 1 0 0 1 1

ASCII Character Set

7-bit Characters

d6 d5 d4 d3 d2 d1 d0 0 0 x x x x x Control Characters 0 1 x x x x x Numbers and Punctuation 1 0 x x x x x Upper Case Characters 1 1 x x x x x Lower Case Characters

Ctrl J = Line FeedCtrl M = Carriage ReturnCtrl Q = XONCtrl S = XOFFCtrl Z = End of File

2 Asynchronous Serial PortsSCI0 and SCI1

SCI0 – Uses Port S[1:0]SCI1 – Uses Port S[3:2]

RS-232 TTL Level Converters

TTL – RS-232 ConversionChannel 0RTS = CTSDCD = DTR = DSRRI – No Connection

Channel 1Data Lines Only

TTL – RS-232 ConversionDC to DC Power Supply