The serial port: Alive and well
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 10/1/2007
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The good old serial port is alive and well, even if today’s computers lack the familiar DB-9 connector. Engineers continue to use serial ports to communicate with instruments, ovens, programmable controllers, development boards, and ICs.
Engineers often prefer the serial port when connecting just one instrument to a PC. “At least 50% of my stand-alone instruments still use RS-232,” said Sergey Liberman, consultant at Solidus Integration. “People still use serial ports on Windows 95/98/2000 platforms because they work,” added Chris Harden of EasyDaq when I asked an online forum of test engineers.
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For more comments on the serial port, see my |
Serial ports may have vanished from PCs in favor of USB and Ethernet, but they haven’t vanished from PXI embedded controllers. The figure compares a 1997 PXI controller from National Instruments to its 2007 successor. Over 10 years, one serial port has been replaced by three additional USB ports, but one serial port remains. “Our customers keep asking for a serial port,” said Luke Schreier, precision DC and digital test manager at National Instruments.
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| A 1997 PXI embedded controller (top) has two serial ports. The 2007 version adds three USB ports but still retains one serial port. Courtesy of National Instruments. |
Many microcontrollers provide serial ports because they’re inexpensive to implement. “I use the serial port all the time to send and receive information from my development board,” said Oscar Rivera at Intel.
Measurement instruments and other equipment that now have USB ports may still use serial ports internally. “Many newer instruments use USB-to-RS-232 chips and therefore are still programmed using RS-232,” added Liberman of Solidus Integration. Converter ICs provide a virtual serial port carried over USB so that systems can use a PC’s USB port without requiring a complete redesign to fully implement USB.
Other engineers report that they use Ethernet in conjunction with serial ports to reduce the number of cables in a system. For example, Alvin Moore, measurement systems programmer at Corning Cable Systems, connected several temperature chambers, which have serial ports only, to a PC through an Ethernet hub. He used an Ethernet-to-serial converter for each serial port but needed only one cable to connect them to his computer. Moore used VISA to communicate from his application program to the chambers.
“Serial ports are painful to use but easy for the instrument developer to implement,” said Scott Hannahs, researcher at Florida State University.
Wiring two devices with serial ports may require you to swap the transmit and receive wires (pins 2 and 3). If you have the right cable, then the serial port is easy to use, especially if you’re frequently changing instruments or need to connect just one instrument to a PC.
m.rowe@tmworld.com
For more comments on the serial port, see my “Rowe’s and columns” blog.
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