BASICS OF SERIAL COMMUNICATIONS BIRLA VISHWKARMA MAHAVIDYALAYA ELECTRONICS & TELECOMMUNICATION DEPARTMENT PRESENTING BY: ABHISHEK SINGH AMANDEEP JANGRA ANJARIYA SHREY ANKUR BUSA GUIDED BY : PROF. HIREN PATEL

CONTENT SERIAL AND PARALLEL DATA TRANSFER HALF, FULL-DUPLEX TRANSMISSION. SYNCHRONOUS & ASYNCHRONOUS COMMUNICATION START AND STOP BITS DATA TRASFER RATE RS232 STANDARDS RS232 PINS DATA COMMUNICATION CLASSIFICATON EXAMINING OF RS232 HANDSHAKING SIGNALS x86 PC COM PORTS

BASIC OF SERIAL COMMUNICATION Serial versus Parallel Data Transfer

HALF AND FULL-DUPLEX TRANSMISSION

SYNCHRONOUS & ASYNCHRONOUS COMMUNICATION SYNCHRONOUS METHOD SYNCHRONOUS METHOD TRANSFER A BLOCK OF DATA AT A TIME. ASYNCHRONOUS METHOD ASYNCHRONOUS METHOD TRANSFERS A SINGLE BYTE AT A TIME.

ASYNCHRONOUS SERIAL COMMUNICATION  WITH ASYNCHRONOUS COMMUNICATION, THE TRANSMITTER AND RECEIVER DO NOT SHARE A COMMON CLOCK Transmitter Receiver + 1 byte-wide Data Data – 1 byte-wide Data The Receiver  Extracts the data using its own clock  Converts the serial data back to the parallel form after stripping off the start, stop and parity bits THE TRANSMITTER  SHIFTS THE PARALLEL DATA ONTO THE SERIAL LINE USING ITS OWN CLOCK  ALSO ADDS THE START, STOP AND PARITY CHECK BITS Add: Start, Stop, Parity Bits Remove: Start, Stop, Parity Bits

ASYNCHRONOUS SERIAL COMMUNICATION  ASYNCHRONOUS TRANSMISSION IS EASY TO IMPLEMENT BUT LESS EFFICIENT AS IT REQUIRES AN EXTRA 2-3 CONTROL BITS FOR EVERY 8 DATA BITS  THIS METHOD IS USUALLY USED FOR LOW VOLUME TRANSMISSION

SYNCHRONOUS SERIAL COMMUNICATION IN THE SYNCHRONOUS MODE, THE TRANSMITTER AND RECEIVER SHARE A COMMON CLOCK THE TRANSMITTER TYPICALLY PROVIDES THE CLOCK AS A SEPARATE SIGNAL IN ADDITION TO THE SERIAL DATA Transmitter Receiver Data Clock THE RECEIVER  EXTRACTS THE DATA USING THE CLOCK PROVIDED BY THE TRANSMITTER  CONVERTS THE SERIAL DATA BACK TO THE PARALLEL FORM THE TRANSMITTER  SHIFTS THE DATA ONTO THE SERIAL LINE USING ITS OWN CLOCK  PROVIDES THE CLOCK AS A SEPARATE SIGNAL  NO START, STOP, OR PARITY BITS ADDED TO DATA 1 byte-wide Data

START AND STOP BITS IN THE ASYNCHRONOUS METHOD, EACH CHARACTER IS PLACED BETWEEN START AND STOP BITS. THIS IS CALLED FRAMING. IN DATA FRAMING FOR ASYNCHRONOUS COMMUNICATIONS THE DATA SUCH AS ASCII CHARACTERS ARE PACKED BETWEEN START AND STOP BIT. THE START BIT IS ALWAYS ONE BIT, BUT THE STOP BIT CAN BE ONE OR TWO BITS.

DATA TRASFER RATE  THE RATE OF DATA TRANSFER IN SERIAL DATA COMMUNICATION IS STATED IN bps. ANOTHER WIDELY TECHNOLOGY FOR bps IS BAUD RATE.  THE DATA TRANSFER RATE OF A GIVEN COMPUTER SYSTEM DEPENDS ON COMMUNICATION PORTS INCORPORATED INTO THAT SYSTEM.  FOR E.G. THE EARLY IBM PC COULD TRANSFER bps. WHERE AS IN PRESENT PC

RS232 STANDARDS  TO ALLOW COMPATIBILITY AMONG DATA COMMUNICATIONS EQUIPMENT MADE BY VARIOUS MANUFACTURES, AN INTERFACING STANDARD CALLED RS232 WAS SET BY THE ELECTRONICS INDUSTRIES ASSOCIATIONS (EIA) IN  RS232 IS ONE OF THE MOST WIDELY USED I/O INTERFACING STANDARDS.  STANDARD WAS SET LONG BEFORE THE ADVENT OF TTL LOGIC FAMILY HOWEVER ITS I/O LEVELS ARE NOT TTL COMPATIBLE.  IN RS232 A 1 IS REPRESENTED BY -3V TO -25V WHILE 0 BIT IS +3V TO +25V.  MAX232 IS USED FOR CONVERT THE TTL LOGIC LEVEL TO THE RS232 VOLTAGE LEVEL.

RS232 PINS  DB25 REFERS TO THE PLUG CONNECTOR (MALE) DB25S FOR THE SOCKET CONNECTOR (FEMALE).  BECAUSE NOT ALL THE PINS WERE USED IN PC CABLES IBM INTERDUCE DB-9 VERSON OF THE SERIAL I/O STANDARD WHICH USES ONLY 9 PINS.

IT SHOWS PINS FOR RS232 FOR DB25 CONNECTOR

TYPICALLY, THE CONNECTOR IS “MALE” FOR DTE EQUIPMENT AND “FEMALE” FOR DCE EQUIPMENT.

DATA COMMUNICATION CLASSIFICATON  CURRENT TERMINOLOGY CLASSIFIES DATA COMMUNICATION EQUIPMENT AS DTE (DATA TERMINAL EQUIPMENT) OR DCE (DATA COMMUNICATION QUIPMENT). DTE REFERS TO THE TERMINAL AND COMPUTERS THAT SENDS AND RECEVIE DATA WHILE DCE REFERS TO COMMUNICATION EQUIPMENTS SUCH AS MODEMS DATA RESPONSIBLE FOR TRANSFERRING THE DATA.  THE SIMPLEST CONNECTION BETWEEN PC AND MICROCONTROLLER REQUIRES MINIUM OF 3 PINS, TX, RX AND GRND

EXAMINING OF RS232 HANDSHAKING SIGNALS  TO ENSURE FAST AND REALIABLE DATA TRANSMISSION BETWEEN TWO DEVICES THE DATA TRANSFER MUST BE COORDINATED.  RS232 CONNECTOR ARE USED FOR HANDSHAKING SIGNALS  THEY CAN BE BYPASSED BECAUSE THEY ARE NOT SUPPORTED BY THE AVR UART CHIP. DTR (DATA TERMINAL READY). DSR (DATA SET READY). RTS (REQUEST TO SEND). CTS (CLEAR TO SEND). DCD (DATA CARRIER DETECT). RI (RING INDICATOR).

DTR AND DSR ARE USED BY PC AND MODEM INDICATE THAT THEY ARE ALIVE AND WELL, IT IS RTS AND CTS THAT ACTUALLY CONTROLS THE FLOW OF DATA. WHEN THE PC WANTS TO SENDS DATA IT ASSERT RTS, AND INRESPONSE THE MODEM IF IT IS READY TO ACCEPT THE DATA, SENDS BACK CTS.

x86 PC COM PORTS  THE x86 PCs USED TO HAVE TWO COM PORTS.  BOTH COM PORTS WERE RS232 TYPE CONNECTORS.  COM PORTS WERE DESIGNED AS COM 1 AND COM 2.  RECENTLY ONE OF THESE HAS BEEN REPLACE WITH THE USB PORT, AND COM 1 IS THE ONLY SERIAL PORT AVAILABLE.  IN ABSENCE OF COM PORT, WE CAN USE COM TO USB CONVERTER MODULE.