hands-on data communications, networking & tcp/ip troubleshooting

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Hands of Data Communications, Networking

& TCP/IP Troubleshooting

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Topics Basics of serial communication RS-232 RS-422 RS-485


Serial Communication Data is sent and received one bit at a time over

a communication channel. Serial ports

9 pin and 25 pin Used to communicate with terminals and

peripheral devices Also known as COM port, controlled by

UART


Parallel Communication

8 (or 16 or 32) bits are sent and received simultaneously

Sent over a bus comprising 8 (or 16 or 32) channels, one for each bit.

Usually used within a device.


Connector – Types

Types of serial port connectors


DTE vs. DCE

Devices that use serial cables for their communication DTE

Data Terminal Equipment E.g. computers, printers Transmits on Pin 2

DCE Data Communications Equipment E.g. modems Transmits on Pin 3


Asynchronous vs. Synchronous

Asynchronous No clock sent Level sync Character transfer Susceptible to noise Slow Short lengths

Synchronous Clock sent Edge sync Packet transfer Resistant to noise Fast Long distances


Serial Communication – Keywords

Handshaking - a procedure used to check the link between DTE & DCE before transmitting data

Baud Rate Transmission speed Number of bits that are actually being sent over the serial

link

Type of Cables Modem Cable Null Modem Cables


Modem Cable

Signal Description9-pin DTE

25-pin DCE

Remarks

Carrier Detect (CD) 1 8 From Modem

Receive Data (RD) 2 3 From Modem

Transmit Data (TD) 3 2 From Terminal/Computer

Data Terminal Ready (DTR) 4 20 From Terminal/Computer

Signal Ground (SG) 5 7 From Modem

Data Set Ready (DSR) 6 6 From Modem

Request to Send (RTS) 7 4 From Terminal/Computer

Clear to Send (CTS) 8 5 From Modem

Ring Indicator (RI) 9 22 From Modem

RS-232 Pinouts DB9 to DB25


Null Modem Cables

Connecting 25 pin to 25 pin for Null Modem

Signal description 25-pin 25-pin Signal description

Receive Data 3 2 Transmit Data

Transmit Data 2 3 Receive Data

Data Terminal Ready 20 6+8Data Set Ready + Carrier

Detect

System Ground 7 7 System Ground

Data Set Ready + Carrier Detect

6+8 20 Data Terminal Ready

Request to Send 4 5 Clear to Send

Clear to Send 5 4 Request to Send


Null Modem Cables

Connecting 9 pin to 9 pin for Null modem

Signal description 9-pin 9-pin Signal description

Receive Data 2 3 Transmit Data

Transmit Data 3 2 Receive Data

Data Terminal Ready 4 6+1Data Set Ready + Carrier

Detect

System Ground 5 5 System Ground

Data Set Ready + Carrier Detect

6+1 4 Data Terminal Ready

Request to Send 7 8 Clear to Send

Clear to Send 8 7 Request to Send


RS-232 Standard Specifies the method of connection of a DTE and a

DCE. A DCE receives data from the DTE and retransmits it to

another DCE via a data communications channel such as a telephone link.


RS-232 Connections

Connection between DTE and DCE using DB-25 connectors


Voltage Levels


RS-232 Transmitters & Receivers


Half Duplex Operational Sequence of RS 232


RS-422 Interface Standard

Defines a balanced, or differential, data communications interface

Uses two separate wires for each signal Permits very high data rates Minimizes problems with varying ground potentials


The EIA-422 Balanced Line Driver Connections


EIA 422 Voltages vs. Real Life

EIA voltages: ±6 volts to ±2 volts In real systems the voltage is between ±5 volts

and ±.2 volts Often the same chips that are used for 485

systems are used for 422 Typical measured voltage is approximately ±2

volts


EIA - 422 vs. Real Life

Simplex

10Mbps

Differential 10 devices

Half or full duplex

No speed defined Differential Point to point


RS-485 Interface Standard

Most versatile EIA standard Distances of up to 1200m Data rates of up to 10Mbps 32 line drivers 32 line receivers


RS-485 RS-485 is the most common voltage standard in use today

for multi-drop communication systems. This is because …

It is very resistant to noise It can send data at high speeds And can go long distances


Two-Wire Multidrop


Four Wire Network


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