I think I'm turning into a grumpy old man, but where are the com ports on my new laptop? The domestic market's embrace of USB does not however mean that the COM port is dead.
Serial communication was originally developed for the teletype (nickname for a teletypewriter and trademark of the Teletype Corporation USA), an electro-mechanical marvel that emerged in the 1920's for transmitting messages from one point to another. Some even used punched paper tape so you could relay information output from one teletype and feed the strip into another.
Teletypes were adapted as the means of getting information into and out of early computers and in 1969 the RS-232-C standard emerged. The first VDU terminals were developed to be compatible with the old mechanical teletypes and the RS-232 protocol along with start/stop and parity bits was reborn into our computer age as the COM port.
The ability for RS-232 to be implemented mechanically made it easy to synthesize electronically. The protocol's simplicity meant that unsophisticated devices could be controlled without internal firmware and led to its widespread adoption in industrial automation.
Speed and elegance eventually inspired the USB protocol and the concept of universal 'plug-and-play'. USB devices identify themselves upon connection to a host OS which then configures itself to communicate with that device by installing the appropriate drivers or by 'graceful failure', prompting the user to insert a disk.
USB is an unnecessary complication in dedicated environments such as a vehicle installation. A taxicab may have a taximeter that communicates its fare and tariff information via RS-232 to a data terminal or printer. These devices need to be compatible but don't require the overhead of plug-and-play intelligence.
Although low cost serial to USB semiconductors may make the concept of a USB taximeter possible, creating the USB host for it becomes a nightmare. Any unit with a USB host socket on it implies acceptance of a whole range of USB devices. Deciding what devices to support, communicating a lack of support to the user (graceful failure), and then installing that support, brings pointless complication and cost.
Like USB, integrating multiple RS-232 devices requires a communications hub. However, because RS-232 is not 'universal', integration may require some processing and device configuration via a simple human interface. The demand for more elaborate RS-232 environments has now prompted the emergence of devices like the Datax3 terminal http://www.datax3.com and the Lynx communications hub from Diplomat Ltd. which fills the gap between multiple serial devices and an ergonomic interface flexible enough to cater for interaction with that environment.
USB is great for the domestic computer market but in dedicated environments the traditional serial RS-232 communications port is still very much alive.
This article and others can be found at http://www.diplomat.co.uk
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