Serial Io11

Basics of serial communication

PROCESSO R (PARALLEL )

PARALLEL TO SERIAL

SERIAL TO PARALLEL

DEVICE MODEM (SERIAL)

CLK

TRANSMIT TER

SYNC

SYNC

RECEIVER

DATA

ASYNCHRONOUS TRANSMISSION Start and stop bits

SYNCHRONOUS

• BLOCK OF DATA TRANSMITTED ALONG WITH SYNC INFORMATION • HIGH SPEED TRANSMISSION

ASYNCHRONOUS •CHARACTER CARRIES INFORMATION WITH START AND STOP BITS •WHEN NO DATA IS TRANSMITTED RECEIVER STAYS AT LOGIC 1 CALLED MARK ; LOGIC 0 CALLED SPACE •TRANSMISSION STARTS WITH ONE START BIT AND ONE OR MORE STOP BITS . THIS IS FRAMING

Serial Interfaces: RS-232 •DB25S is a 25 pin connector with full RS-232 functionality •The computer socket has a female outer casing with male connecting pins •The terminating cable connector has a male outer casing with female connecting pins

TTL to RS-232

Types of equipment DTE Data Terminal Equipment Originally applied to CRT terminals or other input devices Today, DTE mainly applies to a computer DCE Data Communication Equipment Originally applied to modems or similar communications equipment  Still applies today A modem is a device that converts a digital signal (e.g. from an RS232 interface) to an analogue signal for transmission over a traditional telephone line (MODEM: MOdulator-

VOLTAGE LEVEL +3V TO +15 V LOGIC 0

BUT USUSALLY LOGIC 1  +12V LOGIC 012V ????!!!!!!

VOLTAGE LEVEL -3V TO -15 V LOGIC 1

YEP…. THATS RIGHT….. HERE WE USE NEGATIVE TRUE LOGIC

• TO MAKE RS 232 COMPATIBLE WITH TTL LOGIC , • VOLTAGE TRANSLATORS CALLED LINE DRIVERS & LINE RECEIVERS ARE USED

RS232 pins

SIGNA LS OF RS232

11 bits required to send a single character (10 if one stop bits are used)  Bit rate (bits/sec): actual rate at which bits are transmitted Baud rate: rate at which the signalling elements, used to represent bits, are transmitted

DTE 2 MICRO COMPUT3 ER 7

TX

RX 2

RX

DCE

TX 3 GND

MODEM 7

2

DTE

3

7

TX

TX 2

RX

RX 3 GND

7

DTE

Typical System Connections

7

7

SERIAL INTERFACES : 8251A USART The functions and requirement for SERIAL I/O are, Input port & Output port for interfacing DATA TX MPU converts parallel to serial DATA RX  MPU converts serial to parallel Synchronization between MPU and slow peripheral

USART – Universal Synchronous /Asynchronous Receiver/ Transmitter

It incorporates all the above features in a single chip and other sophisticated functions for serial communication. It is a programmable device i.e its functions and specifications for serial i/o can be determined by writing instructions to its internal registers

PIN

DESCRIPTION

PIN

DESCRIPTION

D7-D0

DATA BUS

C/D’

CONTROL/DATA

RD’

READ COMMAND

WR’

WRITE COMMAND

CS’

CHIP SELECT

CLK

CLOCK PULSE

RESET

RESET

TxC’

TRANSMITTER CLOCK

TxD

TRANSMITTER DATA

RxC’

RECEIVER CLOCK

RxD

RECEIVER DATA

RxRDY

RECEIVER READY

TxTDY

TRANSMITTER READY

DSR’

DATA SET READY

DTR’

DATA TERMINAL READY

SYNDET/ SYNC DETECT/ BD BREAK DETECT

RTS’

REQUEST TO SEND DATA CTS’

CLEAR TO SEND DATA

TxE

TRANSMITTER EMPTY

+5V SUPPLY

GND

GROUND

Vcc

SIX INPUT SIGNALS

THREE BUFFER REGISTERS • STATUS REG. •CONTROL REG •DATA REG.

 RESET – Reset  LOGIC 1  forces 8251 to RESET and enters into idle mode  CLK - clock  REFERS TO SYSTEM CLOCK Necessary for communication with the processor

8251 mode register- MODE WORD

PARITY CONTROL X0 – NO PARITY 01 – ODD PARITY 11 – EVEN PARITY

Command Register

Status Register

MPU INFORMS 8251 – MODE, BAUD, STOP BITS, PARITY CONTROL WORDS TO BE LOADED FROM MPU TO 8251

OPERATION FLOW