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Digital Communication
10 questions By Tony R. Kuphaldt
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Question 7 of 10
Shown here are three different telegraph circuits. Determine which of these could be classified as simplex, full-duplex, and half-duplex, in terms of serial data transmission:
Reveal answer- Simplex: one-way communication
- Half-duplex: two-way communication, one way at a time.
- Full-duplex: two-way communication, both ways simultaneously.
Follow-up question: trace all currents in these circuits using conventional flow, and then electron flow.
Notes:I could have just asked for definitions here, but relating these concepts to real circuits, however simple, carries with it more educational benefit. It is also important to show students that the basic concept of digital communication is really no more complex than the old telegraph, just faster.
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Question 8 of 10
An early form of digital, serial data communication was Morse code. Explain what “Morse code” is (or was), and how it compares to more modern codes such as ASCII.
Reveal answerMorse code was a simple convention used to represent alphanumeric characters for telegraph data transmission. At first, human operators served the task of parallel-to-serial-to-parallel data converters, but then machines were built to do this automatically.
Notes:An interesting feature of Morse code likely not recognized by your students is inherent compression. Because some Morse characters are shorter than others (fewer pulses) as opposed to ASCII where all characters are the same length, messages sent in Morse tend to require fewer bits than messages sent in ASCII.
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Question 9 of 10
An important performance parameter of digital communications networks is the number of bits per second (bps) of data it can handle. Unfortunately, a different term called baud is often used interchangeably with bps. Define what “baud” is, and how it differs from “bits per second.”
Reveal answer“Baud” technically refers to the number of logic level transitions (low-to-high or high-to-low) per second on a network, while “bps” actually refers to the number of data bits transmitted per second. For a specific application where the two terms significantly differ, research a method of data modulation known as Manchester encoding.
Notes:While some may argue the difference to be academic, I believe that precision of language and precision of thinking are closely related. The person who does not recognize the difference between “baud” and “bps” most likely knows little about how digital information is encoded for serial transmission. Of course, this is the ultimate issue - understanding how digital data is transmitted. So while we’re at it, we might as well address a common mis-use of language and gain a deeper understanding of how things work, right?
