Lecture 8 Modems Converts analog signals to digital

Lecture 8: Modems (Converts analog signals to digital and vice-versa) 1 nd semester 1438 -1439 By: Adal ALashban 1

Outline - Modulator “converts digital information to analog” - Demodulator “converts analog information to digital” - RS-232 Interface 2

Modems - A modem: is a hardware device that allows a computer to send and receive data over a telephone lines. - Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. - A modem converts between these two forms. 3

Basic Principle 0101 4

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Basic Structure 6

Classification of Modems - Range - Line Type - Operation Mode - Synchronization - Modulation - Data Rate 7

Range - Short Haul - Voice Grade - Wide Band Line Type - Dial-up - Leased - Private 8

Operation Mode - Simplex - Half-Duplex - Full-Duplex Modulation - AM - FM - PM - TCM 9

Cable Modem - Cable Modems make access to TV cable, and let you get high-speed internet access. - Availability is still limited in many areas, but is growing rapidly. 10

External Modem - It usually plug in through a serial port, or a USB port. - External modems cost the most, but have the benefits of being easily installed. - Also plugs into telephone line. - External power supply is needed. - Holder case is required. - Often they have the indicators that tell the status of your connection there is one standard interface for connecting external modems to computers called RS-232. 11

Typical Indicators on External Modems Front Panel - HS = High speed - AA = Auto answer - CD = Carrier detect - OH = Off hook - RD = Received data - SD = Send data - TR = Terminal ready - MR = Modem ready 12

Internal Modem - It can insert into a vacant expansion slot. - No external power supply is needed. - No holder case is required. - Least expensive at given speed. - Incompatible with different kind of PCs. - These modems go inside the computer, and usually plug directly into the motherboard. 13

ISDN Modem - ISDN: is an abbreviation for Integrated Services Digital Network. - There is no such thing as a noisy or fuzzy line. - Always runs at 64 kbps. - Ability to bond multiple "B" channels to get speeds of 128 kbps. - Call setup is very fast (dialing, handshake and authentication), usually under 2 seconds (compared with 15 seconds at least for most analog modems). - Ability to get 2 calls at the same phone number (one line is for voice, and the other line for your internet connection). 14

Wireless Modem - Convert digital data into radio signals and back. - Support a maximum data transmission rate of 19. 2 Kbps (kilobits per second). - Wireless modems can be used up to 20 -30 miles (30 -50 KM). - Operation is in the 900 MHz and 2. 4 GHz. - Modem names include: Breese. LINK, LATNET-Radio Data Links, Air. Link Wireless Modems, and Open Minds. 15

DSL Modem - DSL Modems: DSL (Digital Subscriber Line) service is usually offered through the phone the company/ISP. - You can leave your Internet connection open and still use the phone line for voice calls. - The speed is much higher than a regular modem (up to 1. 5 Mbps ) - DSL doesn't necessarily require new wiring; it can use the phone line you already have. 16

Modem Speed - The Modulation Speed - The Serial Port Speed Note: - Modem speed is rated in bps (bits per second). - So a 56 k modem transmits at 56, 000 bits per second in theory. - While 8 bits make a byte, and 1024 bits equal one kilobits, a 56 k modem will transmit a maximum of approximately 7 kilobytes of information every second. - A modem will never connect higher than what it is rated for. 17

Modem Installation - Modem Cable Selection. - Selection of Port. 18

What is RS 232 - RS: means Recommended Standard. - RS 232 uses both synchronous and asynchronous communication. - In microcontrollers like ATmel 89 C 51 asynchronous communication is used and it is called as UART – universal asynchronous receiver and transmitter. PCI Express x 1 card with one RS-232 port 19

Interfacing RS 232 - We need a driver to use the RS 232 with microcontroller. - That driver turned out to be MAX 232. - It is a 16 PIN Ic which is used to interface RS 232 with any other devices. - The transmission speed in the RS 232 is called as baud rate. 20

Setting Serial Port - In microcontroller there are some special function registers which are allocated to control the serial communication. - The list of registers which is used to control the serial port are: SCON PCON SBUF 21

Any Questions ?