Serial communications products include a variety of devices that send data serially, or one bit at a time. Serial and parallel communications are two methods of sending data between two microprocessors or computer devices. Parallel communication involves sending data all at once using multiple channels (wire conductors, optical fibers, etc.). While parallel data transfer is capable of transmitting large amounts of data very quickly, its need for multiple channels requires more space and resources and may result in crosstalk interference between channels.

Serial vs. parallel communication. Image credit: What When How

Because serial data transfer requires only one channel, serial systems tend to be smaller and cheaper to produce when used in large-scale networks. Serial technology is also beginning to supersede parallel in smaller short distance networks due to technological improvements in signal integrity and transmission speed.

Product Types

The Engineering360 SpecSearch database contains information about numerous serial communications devices.

• Adapters provide one or more serial ports to a host computer.
• Data converters convert data from one serial standard to another, and may also provide signal isolation and/or amplification as well as noise reduction features.
• Hubs connect serial devices such as industrial instruments, point-of-sale (POS) systems, and barcode printers to an existing area network.
• Multiplexers funnel multiple serial signals into a single channel.
• Routers connect subnetworks and can be used to reduce a large network into several smaller subnetworks. Routers may cause longer transmission delays and have lower throughput rates.
• Servers allow serial devices to be connected to an area network without the use of a personal computer (PC).

Protocol

Communications protocols include formats and rules for telecommunication systems. RS-232, RS-422, and RS-485 are all important serial protocols. A serial device may feature multiple, selectable ports involving any of these three protocols. Other important serial protocols include Serial Peripheral Interface (SPI), I²C, Microwire, and 1-wire.

• RS-232 was established in 1960 by the Electronics Industries Association (EIA) and is the most common input/output interface standard. Most industrial serial applications use RS-232. The typical transmission speed for this standard is 9600 bits per second (bps) at 15 meters.

• RS-422 communication supports high-speed transmissions over a much longer distance than RS-232, albeit with less signal line. Also unlike RS-232, RS-422 supports multipoint connections. RS-422 devices can transmit at up to 110 kilobits per second (kbps) at 1.2 kilometers.

• RS-485 uses three way transmissions and is often suitable in applications where a single controller must interface with multiple devices.

Connectors

For information related to serial connection methods, please see the Connectors portion of the Serial Adapters Selection Guide on Engineering360.

References

TalTech - Introduction to Serial Communications

Image credits:

Endress+Hauser, Inc. | Moxa Inc.