ECE 371- Unit 11 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 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 charData char Header information Data char etc Synchronous Serial Data Transmission Format OR Data char

CLASSES OF SERIAL DATA APPLICATION COMPUTER TO PERIPHERAL DEVICE COMPUTER TO COMPUTER

Computer System Peripheral Device Serial data Handshaking Signals Ground Half-duplex Serial Data Interface Between Computer and Peripheral Device

Computer System Peripheral Device Serial data Handshaking Signals Ground Full-duplex Serial Data Interface Between Computer and Peripheral Device

Computer (DTE) Modem Telephone System Modem Computer (DTE) Serial Data Communication Between Computers, Using Modems RS-232 Standard Interface RS-232 Standard Interface DCE Data Communication Equipment DTE = Data Terminal Equipment RS-232 is a Standard Interface between DTE and DCE

Laptop COM1 Port CPU Asynchronous Serial 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 ≤ V 1 ≤ -5 volts Logic “0”: +5 volts ≤ V 0 ≤ +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 Formats See 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 = 0b = 0x41 ASCII Code for Letter B = 0b = 0x42 ASCII Code for Digit 1 = 0b = 0x31 Idle Start LSB MSB Stop A = B = =

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 Feed Ctrl M = Carriage Return Ctrl Q = XON Ctrl S = XOFF Ctrl Z = End of File

2 Asynchronous Serial Ports SCI0 and SCI1 SCI0 – Uses Port S[1:0] SCI1 – Uses Port S[3:2]

RS-232 TTL Level Converters

TTL – RS-232 Conversion Channel 0 RTS = CTS DCD = DTR = DSR RI – No Connection Channel 1 Data Lines Only TTL – RS-232 Conversion DC to DC Power Supply