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Microcontrollers

Alyssa J. Pasquale, Ph.D.

Chapter 10 Serial Communication

Serial communication occurs when information is sent one bit at a time over a single wire. This is in contrast to parallel communication where information is sent all bits at once, each bit having its own dedicated wire. Serial communication therefore can cause a reduction in the number of wires required to transmit and receive information. The schematic difference between serial and parallel communication is shown in Figure 10.0.1. In this diagram, each transmitter sends 8 bits of data to the receiver.
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On the left, a transmitter (depicted as a rectangle) is shown sending 8 bits of data in parallel to a receiver (depicted as another rectangle). On the right, a transmitter (depicted as a rectangle) is shown sending the same 8 bits of data in serial over one wire to a receiver (depicted as another rectangle). In this serial communication image, the transmitter sends the MSB first and the LSB last.
Figure 10.0.1. Schematic difference between parallel I/O (which uses many wires) and serial I/O (which can use as few as one wire).
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While parallel data transmission allows many bits to be sent simultaneously, it requires as many wires as bits. This can be prohibitive in a microcontroller as the number of I/O ports is quite limited. In addition, parallel I/O can suffer from noise known as crosstalk which occurs when electromagnetic interference between neighboring wires causes signal levels to change unexpectedly.
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With serial communication, data is sent one bit at a time. Using as few wires as possible minimizes crosstalk. There are many features of serial communication that may change the configuration and number of wires required to implement the communication protocol.
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