Download - ECE 371- Unit 10-Part 1
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