Copyright © 2007 Heathkit Company, Inc. All Rights Reserved PC Fundamentals Presentation 45 – Modems

2 Objectives At the end of this presentation, you will be able to:

3 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.

4 Local Exchange Local Exchange Analog Digital

5 Local Exchange Local Exchange Analog Digital Modem

6 Modem-1 PC-1 Modem-2 PC-2 Phone System

7 CPU vs. Phone Line Digital Signal High Speed Parallel Data Analog Signal Low Speed Serial Data

8 Analog Digital 8

9 The 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.

10 Pulse Amplitude Modulation (PAM)

11 Each Amplitude Level Represents Two Bits

12 0º Phase Shift 90º Phase Shift 180º Phase Shift 270º Phase Shift 12

13 Baud 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.

14 Low Speed 14 High Speed

Parallel Serial

16 The UART Universal Asynchronous Receiver/Transmitter The 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.

17 Making the CPU and Phone Line Compatible (Transmit). CPU UART Modem Phone Line Phone Line 1. High Speed to Low Speed 2. Parallel to Serial Digital to Analog Buffer Memory Buffer Memory

18 Making the CPU and Phone Line Compatible (Receive). UART Modem Phone Line Phone Line 1. Serial to Parallel 2. Low Speed to High Speed Analog to Digital CPU Buffer Memory Buffer Memory

19 Two Types of Modems Internal – ISA or PCI board that fits inside the computer. External – Stand-alone box. Connects to one of the COM Ports.

20 Internal Modem CPU UART Function Modem Function Phone Line Internal Modem

21 CPUUART External Modem Phone Line Motherboard

22 CPUUART External Modem Phone Line Mother- board I/O Adapter Card

23 Modulation 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

24 V.42 Error-Correction Standards Link Access Procedure for Modems (LAPM) Microcom Networking Protocol – 4 (MNP-4)

25 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.

26 The COM Port Also called the Serial Port or RS-232 Port The 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.

27 9-Pin Serial Port25-Pin Serial Port

28 Standard Modem COM Port Settings COM PortIRQI/O Address (Hex) COM1403F8 COM2302F8 COM3403E8 COM4302E8

29 CPU UARTModem I/O Memory COM1 IRQ4 03F8

30 CPU UARTModem I/O Memory COM2 IRQ3 02F8

kbps kbps 33.6 kbps kbps kbps

32 UART Speed Determines the Serial Port speed UART chip can reach speeds of 256 kbps UART chip can reach speeds of kbps UART was supplied with the original IBM XT machine.

33 RJ-11 RJ-45 Internal Modem Internal Modem NIC

Copyright © 2007 Heathkit Company, Inc. All Rights Reserved PC Fundamentals End