presentation 45 – modems
DESCRIPTION
Presentation 45 – Modems. Objectives. At the end of this presentation, you will be able to:. Explain three problems involved in sending data over ordinary telephone lines. Explain the purpose of the Modem and the UART and briefly explain how each works. - PowerPoint PPT PresentationTRANSCRIPT
Copyright © 2007 Heathkit Company, Inc. All Rights Reserved
PC Fundamentals
Presentation 45 Presentation 45 –– Modems Modems
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ObjectivesObjectives
At the end of this presentation, you will be able to:
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Explain three problems involved in sending data over ordinary telephone lines.
Explain the purpose of the Modem and the UART and briefly explain how each works.
Match the Modem speed to its “V dot” standard.
Recognize the “V dot” standards for Modem error correction and compression.
Match the Serial Port speed to its UART chip type.
List the de facto standards for the resources assigned to Serial Ports COM1 through COM4.
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Local Exchange
Local Exchange
AnalogAnalog
DigitalDigital
DigitalDigital
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Local Exchange
Local Exchange
AnalogAnalog
DigitalDigital
DigitalDigital
ModemModem ModemModem
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Modem-1
PC-1
Modem-2PC-2
Phone System
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CPU vs. Phone LineCPU vs. Phone Line Digital Signal High Speed Parallel Data
Analog Signal Low Speed Serial Data
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Analog
Digital
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The ModemThe Modem
Modulator / Demodulator
Converts the digital signals from the computer into the analog signals required by the telephone line.
Converts the analog signals from the telephone line into the digital signals required by the computer.
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Pulse Amplitude Modulation (PAM)
1 0 1 1 0 1
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11
Each Amplitude Level Represents Two Bits
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0001
10
11
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0º Phase Shift 90º Phase Shift
180º Phase Shift 270º Phase Shift
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BaudBaud
Baud - A single state change of the analog signal.
Baud Rate - The number of times per second that the analog signal changes state.
In early modems, one baud usually represented one bit.
In today’s modems, one baud represents more than one bit.
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Low Speed
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High Speed
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10101110
ParallelParallel
10101110 SerialSerial
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The UARTThe UART
Universal Asynchronous Receiver/TransmitterThe heart of the Serial (COM) port.Converts the parallel data required by the CPU
into the serial data required by the serial port.Converts the serial data received at the serial
port into the parallel data required by the CPU.
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Making the CPU and Phone Line Making the CPU and Phone Line Compatible (Transmit).Compatible (Transmit).
CPUCPU
UARTUART ModemModem Phone Line
Phone Line
1. High Speed to Low Speed
2. Parallel to Serial
Digital to Analog
BufferMemoryBuffer
Memory
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Making the CPU and Phone Line Making the CPU and Phone Line Compatible (Receive).Compatible (Receive).
UARTUART ModemModem Phone Line
Phone Line
1. Serial to Parallel
2. Low Speed to High Speed
Analog to Digital
CPUCPU
BufferMemoryBuffer
Memory
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Two Types of ModemsTwo Types of Modems
Internal – ISA or PCI board that fits inside the computer.
External – Stand-alone box. Connects to one of the COM Ports.
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Internal ModemInternal Modem
CPUUART
FunctionModem Function
Phone Line
Internal Modem
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CPU UART External Modem
Phone Line
Motherboard
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CPU UART External Modem
Phone Line
Mother-board
I/OAdapter
Card
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Modulation StandardsModulation Standards
V.22 – 1200bps standard V.22bis – 2400bps standard V.32 – 9600bps standard V.32bis – 14,400 standard V.FC – 28,800 standard V.34 – 33,600 standard V.90 – 56kbps download, 33.6 kbps upload
standard V.92 – 56kbps download/upload standard
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V.42 Error-Correction StandardsV.42 Error-Correction Standards
Link Access Procedure for Modems (LAPM)
Microcom Networking Protocol – 4 (MNP-4)
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V.42bis Compression Standard.V.42bis Compression Standard.
Uses a compression technique to reduce the size of out going data.
Can compress data up to about 4 to 1. For example, a 33,600-bps Modem could
transfer data at a rates up to about 134,400 bps.
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The COM PortThe COM Port
Also called the Serial Port or RS-232 PortThe link between the computer and the Modem.The external Modem connects to the COM port
on the back of the computer via a serial cable.The internal Modem has a built-in COM port
that duplicates the function of the external COM port.
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9-Pin Serial Port25-Pin Serial Port
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Standard Modem COM Port Standard Modem COM Port SettingsSettings
COM Port IRQ I/O Address (Hex)
COM1 4 03F8
COM2 3 02F8
COM3 4 03E8
COM4 3 02E8
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CPU
UART ModemI/O
Memory
COM1
IRQ4
03F8
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CPU
UART ModemI/O
Memory
COM2
IRQ3
02F8
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134.4kbps
134.4kbps
33.6 kbps
33.6 kbps
33.6
kbp
s
33.6
kbp
s
134.4kbps
134.4kbps
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UART SpeedUART Speed
Determines the Serial Port speed. 16550 UART chip can reach speeds of 256
kbps.16440 UART chip can reach speeds of
115.2 kbps.8250 UART was supplied with the original
IBM XT machine.
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RJ-11RJ-11
RJ-11RJ-11
RJ-45RJ-45
InternalModem
InternalModem
NICNIC
Copyright © 2007 Heathkit Company, Inc. All Rights Reserved
PC Fundamentals
EndEnd