Link This | Email this | Blog This | Comments (0)

Engineers check in on the serial port
August 23, 2007

In "The serial port: it won't go away," I mentioned how engineers continue to use the serial port (RS-232, RS-422, RS-485), even though it's not available on most new PCs. I also posted comments on the popular port to two e-mail user groups, for Agilent VEE and National Instruments LabView. I received numerous comments and even started a few discussions. Here are a few of the comments. I've used names only for those who have granted their permisson.

James Hannah of WiQuest Communications wrote:
"For simple devices, a bare-bones 3-wire serial interface (rx, tx, and ground) is hard to beat. Whether it be communication with a simple hand-held instrument or a semiconductor device with a UART interface, this simple bus still offers a lot of utility. The software is easy to implement and the hardware can be done on a 3-pin header or a DB-9 connector, which are both readily available at the local electronics store for peanuts."

A test engineer from Switzerland who connected a serial port to a 68HC12 microcontroller added:
"The controller was used to tune a 500-MHz phase shifter and a 1.2 GS/s digital delay line. We successfully adapted existing 68HC12 assembler code to interpret commands at the serial port and control the connected PCBs. The unit was controlled via an ethernet-to-serial converter somewhere in an accelerator tunnel."

Several engineers expressed concern about the quality of USB-based serial ports because you need a driver for most test instruments and idustrial controls. Jason Dunham of ShotSpotter wrote:
"Now that laptops are so popular and most don't have serial ports, a USB-based serial port is essential. There is a wide variation in quality. I've been burned too many times."

Scott Hannahs, a researcher at Florida State University and the LabView group administrator, went further.
"USB needs a driver for each device. Try programming USB-RAW VISA sockets and you will soon find out why!  A single USB 1.1 device will bring a whole USB 2.0 group down to USB1 speeds [12 Mbps].  Precise timing is impossible. [There are] No well defined communication protocol."

A test engineer from Japan spoke of the main reason engineers still use the serial port:
"I will keep using it as long as my instrumentation keeps working and instruments with the serial port are on the market. I have connected DC power source and PLCs (programmable logic controllers) that control mechanical systems to serial ports. Lately I connected an automotive ECU (electr ical control unit) to a serial port in order to test it.There are many PCs that have USB but do not have a serial port. So, I sometimes use USB-to-Serial converters."

Further proof came recently when a company previewed for me a new benchtop test instrument that has just one communications port: serial RS-232.

I will cover the serial port again the October 2007 print issue of Test & Measurement World. Look for my "Tech Trends" column.

Posted by Martin Rowe on August 23, 2007 | Comments (0)