So long, old friends

The venerable serial and parallel ports have started to disappear from PCs. New desktop PCs come with one rather than two serial ports, and many new laptop PCs lack such ports altogether.

Because the test industry lags behind the PC industry by several years, however, lab and industrial test equipment with these I/O ports live on. Test engineers must find ways to control this equipment from PCs that no longer have the traditional ports. Few instruments use the parallel port, so the focus on support for legacy products falls to the RS-232, RS-422, and RS-485 serial ports.

For connecting PCs to test instruments, the USB and Ethernet ports—with their smaller connector size, easier installation, and greater speeds than serial ports—will reign. "Many lab instruments in use contain serial RS-232 ports," says Dany Cheij, product manager at National Instruments (www.ni.com), "and engineers won't abandon them over a communications port." While you can buy single-port USB-to-RS-232 converters from computer stores, you can also find converters that add up to eight serial ports from one USB port (see figure). Cheij also reports that some engineers are looking to use wireless communication links such as Bluetooth or IEEE 802.11 (WiFi) for instrument communications, although wireless communications still require a serial-port converter.

Peripherals such as the SeaLink from Sealevel Systems adds eight serial ports from one USB port. Courtesy of Sealevel Systems.

Many measurement applications use PCI-bus cards that add serial ports to PCs because engineers often need more than two serial ports. Manufacturers report increased sales of these cards because many desktop PCs now contain just one serial port. Quatech (www.quatech.com) president Steve Runkel predicts that makers of test equipment and other products will use serial ports for many years. But PCI-bus I/O cards may someday lose out to external bus converters because PC makers keep reducing the number of internal expansion slots.

While PCs may lose internal expansion slots, a new external expansion slot may take expansion outside the PC. NewCard should replace CardBus (which replaced PC Card) as an external expansion slot for notebook and desktop PCs. A NewCard standard is under development under the auspices of PCMCIA (www.pcmcia.org) and will use a high-speed serial bus (PCI Express or USB 2.0) rather than a parallel PCI bus to connect peripherals to a computer. PCMCIA reports that it should ratify a NewCard standard this fall, with products appearing about a year later. If NewCard succeeds, you may see NewCard-to-RS-232 converters appear that will keep your test equipment running.

Martin Rowe, Senior Technical Editor m.rowe@tmworld.com