communication systems i cpe 313: micro processors and interfacing
TRANSCRIPT
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Communication Systems I
CPE 313: Micro Processors and Interfacing
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How can information flow frompoint A to point B?
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Morse Code
Can you spell your name?
See http://morsecode.scphillips.com/jtranslator.html for a live demo
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Morse Code in Hollywood
1996 Film
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Fountain of Bits
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How to transmit voice?
Speaker = Sound reproducer Mic = Sound transducerMax Frequency Range:
20-20,000 Hz
Electrical signal in a transmission line
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How Are Phone Connected?
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How are phone conversations connected?
Traditional Switched Network
Each conversation needs a dedicated line. Very expensive to build the network.
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Using Multiplexing Techniques
Frequency Division Multiplexing (FDM)
Many connections can be multiplexed through a single line
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Freqeuncy Channels
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Traditional Telephone Lines Limitthe Sound Frequencies Transmitted
400 – 3,400 Hz
The bandwidth of this line is 3kHz
Can you think of
why?
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Frequency Channels
If the main transmission line has a maximum bandwidth of 1MHz,How many concurrent phone connections can it carry?
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What if we want to send digital data over the phone line?
Can it be done?010111001010111001
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Digital to Analog Encoding
See http://www.iesmarenostrum.com/informatica/zmaterias/ral/flash/digit_modulation.swf for an interactive demo.
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Example: A Traditional Modem
Modem Typical Maximum Speed
56Kbps
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How data is sent with a traditional modem
Traditional Modem
Telephone Network
Home
Internet Gateway
DestinationPhone
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Example II: ADSL Modem
ADSL
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Why is ADSL much faster?
256 Channels of 4 kHz each
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But What About the 4K Bandwidth Limitation?
Splitter ADSL Modem
DSLAM
Telephone Network
Data Network
Home
Digital Subscriber Line Access Multiplexer
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How fast is ADSL?
ADSL = 256 x 4 kHz x 8 bits= 8 Mbps
ADSL2 = 12 Mbps
ADSL2+ = 25 Mbps
*ADSL2+ expands channel frequency from 1.1 to 2.2 MHz
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Serial vs Parallel Transmission
Image © Quatec
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Example of Serial Comm?
Example of Parallel Comm?
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Which Mode is More Common?
Cost. Less cables. Smaller size. Simplicity. Keeping bits aligned in a high-
speed parallel line requires more complex electronics.
Serial
Why?
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The Need for SpeedS
peed
Mbp
s
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Synchronous vs Asynchronous
A B
A B
Synchronous uses a clock line
Asynchronous relies on a common clock on each side
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Playing Catch with a Blind Receiver
If you are the blind catcher, which method would you choose?Method 1: Pitcher throws and sends a signalMethod 2: Pitcher throws every 10 seconds. No signal.
PitcherCatcher
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RS-232 (Serial Communication) Baud Rate
Data bits
Start bit / Stop bits
Parity
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RS-232 Pulses
Letter “V” ASCII = 86 (0101 01102)9600 bps, 8-N-1
Layout: Start Bit, Data Bits, Parity, Stop Bits
* Note: Rs-232 logic pulses are inverted
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RS-232 Pulses
Letter “Y” ASCII = 89 (0101 10012)9600 bps, 8-Odd-1
Layout: Start Bit, Data Bits, Parity, Stop Bits
* Note: Rs-232 logic pulses are inverted
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How about ASCII 255?
Layout: Start Bit, Data Bits, Parity, Stop Bits
The data transmission is unbalanced. Can cause transmission errors.
9600 bps, 8-N-1
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Manchester Encoding (IEEE 802.3)
Bit 1 = Low to High
Bit 0 = High to Low
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Example
Image: Wikipedia
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Data = 255
Manchester Code
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Encode the following transmissions using the Manchester standard
Letter “V” ASCII = 86 (0101 01102)
Letter “Y” ASCII = 89 (0101 10012)