Hands-on Data Communications, Networking & TCP/IP Troubleshooting
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Technology Training that Works
Hands of Data Communications, Networking
& TCP/IP Troubleshooting
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Topics Basics of serial communication RS-232 RS-422 RS-485
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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
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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.
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Connector – Types
Types of serial port connectors
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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
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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
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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
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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
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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
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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
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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.
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RS-232 Connections
Connection between DTE and DCE using DB-25 connectors
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Voltage Levels
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RS-232 Transmitters & Receivers
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Half Duplex Operational Sequence of RS 232
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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
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The EIA-422 Balanced Line Driver Connections
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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
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EIA - 422 vs. Real Life
Simplex
10Mbps
Differential 10 devices
Half or full duplex
No speed defined Differential Point to point
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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
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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
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Two-Wire Multidrop
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Four Wire Network
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