Part 7: Channel Organization
Introduction
This section briefly discusses how data might be sent from one point to another, namely via a
parallel method, or via a serial method. Each technique has its own advantages and disadvantages.
Channel Organization
Data may be transmitted between two points in two different ways. Lets consider sending 8 bits of
digital data (1byte). These bits may be sent all at once (in parallel), or one after the other (serial).
• Parallel
Each bit uses a separate wire. If there is eight bits sent at a time, this will require 8 wires,
one for each data bit. The organization looks likes,
To transfer data on a parallel link, a separate
Line is used as a clock signal. This serves to
Inform the receiver when data is available.
In addition, another line may be used by the
Receiver to inform the sender that the data
Has been used, and its ready for the next data.
In the above diagram, the sender places the data on the data lines, then signals the receiver
that data is available by asserting (sending a pulse) on the DA (Data is available) line. After
reading the state of the data lines, the receiver signals back to the sender that it has
processed the data and is now ready for some more data by asserting the DU (Data used)
line. The sender, upon getting the DU signal, removes the data and sends the next data
element in the same manner.
This exchange of signals such as DA and DU between the sender and the receiver is called
a handshake. These handshake signals allow the sender and receiver to keep synchronized
(work on the same data at the same time in the proper sequence).
Parallel transmission is obviously faster than serial, because more than one bit is sent at a
time. Parallel transmission is good only for short links, and examples are found in all
computers. The address, data and control buses which interface the processor to other
peripherals inside the computer are all parallel buses. In addition, most printers on the PCs
(LPT1/LPT2) use a parallel interface, commonly called the Centronic Interface.
DA
DU
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