RS232

RS 232 SERIAL INTERFACE

SERIAL INTERFACES

Serial transmission involves the sending of data one bit at a time, over a single communication line.

In order to ensure an orderly flow of data between a DTE and

DCE, a standard serial interface is used to interconnect them.

The serial interface coordinates the flow of data, control signals

and timing information between the DTE and the DCE.

One of the advantages of a serial system is that it lends itself to

transmission over telephone lines.

DEFINITON

Officially, RS-232 is defined as the “Interface between data

terminal equipment and data communications equipment using serial binary data interchange.”

RS stands for ‘Recommended Standard”. RS 232

DTE DCE

RS-232 DB9 PORT

HISTORY• In the early 1960s, data communications was thought to mean

digital data exchange between a centrally located mainframe computer and a remote computer terminal, or even between two terminals without a computer involved.

• These devices were linked by telephone voice lines, and therefore required a modem at each end for signal translation.

• RS-232 was first introduced in 1962 by the Radio Sector of the Electronics Industries Association ( EIA ).Today it's widely interpreted as Recommended Standard 232. 

• A standard was needed to ensure reliable data communications, and to enable the interconnection of equipment produced by different manufacturers.

DESCRIPTIONS

The standards specified identify four different descriptions :

Mechanical Descriptions

Electrical Descriptions

Functional Descriptions

Procedural Descriptions

MECHANICAL DESCRIPTION

It specifies a cable with two connectors.

The standard RS-232 cable is a sheath containing 25 wires.

• A DTE is connected to a DCE pin to pin.

• DTEs are most common today

• A DTE can connect to another DTE using a “null modem cable”.

• In this cable the wires are crossed so that input meets the corresponding output.

The DCE equipment connector is male ( plug ) for the connector housing and female ( receptacle ) for the connection pins.

The DTE connector is a female ( receptacle ) housing with male ( plug ) connection pins.

ELECTRICAL DESCRIPTION

• The standard specifies limitations on the voltage levels that the DCE and the DTE can output onto or receive from the cable.

• Voltage leveling circuits should output compatible voltages.

• The transmitting voltage leveler is called driver The receiving voltage leveler is called terminator.

• The difference in the voltage levels between the driver output and

the terminator input is called noise margin.

VOLTAGE SPECIFICATIONS

ELECTRICAL EQUIVALENT CIRCUIT

FUNCTIONAL DESCRIPTION

Based on the function the pins are classified as :

Ground ( signal and chassis ) Data ( transmit and receive ) Control ( handshaking and diagnostic ) Timing ( clocking signals )

RS-232 as a whole is bidirectional but each individual wire ( pin ) is unidirectional.

• There are two full-duplex data channels available with the interface.

• One channel is for primary data – actual information

• The other channel is secondary data – for diagnostic information and handshaking

signals.

• The secondary channel is sometimes used as reverse of backward channel allowing the receive DCE to communicate with the transmit DCE while data are being transmitted in the primary channel.

The specific functions of each of the pins are :

9 , 10 , 11 , 18 , 25 - unassigned

1 , 7 - ground

2 , 3 , 14 , 16 - data

15 , 17 , 24 - timing ( only for synchronous ) others - control and handshake ( 4, 5, 6, 8, 12, 13, 19, 20, 21, 22, 23 )

25 RS-232 PINS

FUNCTIONS OF 25 RS-232 PINS

DB9 PINS

DB9 PIN FUNCTIONS

TRANSMIT TIMING DIAGRAM

INTERFACE FUNCTIONS

FUNCTIONAL BLOCK DIAGRAMS

– Drivers

– Terminators

FUNCTIONAL BLOCK – TRANSMIT CIRCUIT

Pin 1 ( Chassis Ground )

Pin 2 ( TD )

Pin 4 ( RTS )

Pin 5 ( CTS ) RTS / CTS Delay

Pin 6 ( DSR )

Pin 7 ( Signal Ground )

DTE DCE

FUNCTIONAL BLOCK – RECEIVE CIRCUIT

Pin 3 ( RD ) • Data Demodulator•

Pin 8 ( RLSD ) Analog Carrier Detect Circuit

DTE DCE

TIMING DIAGRAM – TRANSMIT STATION

DSR

RTS

RTS / CTS

CTS delay

TD

Analog Training Digitally modulated Carrier Sequence Carrier with data

TIMING DIAGRAM – RECEIVE STATION

RLSD

•

RLSD turn-off Delay

RD

Training Digitally modulated Sequence Carrier with data

Hope at least some data has been

communicated and received successfully !!