Tips & Tricks: Using Port Powered Converters

What Type of Driver Do I Have On My Port?

To determine the type of driver used on a serial port without looking at the ICs, put a 3K ohm load on the driver output line to signal ground and measure the voltage. If possible measure the voltage under both (+) and (-) voltage conditions. These voltage measurements should give values as shown below.

Loop Back Connections

Many port powered converters will have loop back connections, such as RTS connected to CTS. These loop back connections each dissipate about 8.3 mW per input line. The only reason to make these connections is that some software requires these connections. If you have control over the software, change the software so that the loop back conditions are not required. Also, don't complete the loop back connections in the cables you are using. (See Figure 2.)

Summary of Tips

• Connect all port driver lines to the converter.
• Keep all unused port driver lines in positive voltage state.
• Determine if the port can drive the converter (what type of driver).
• Don't terminate the transmission line, if not necessary.
• Don't make loop back connections, if not necessary.

About the Author

Mike Fahrion, director of product management at B&B Electronics is an expert in data communications with 20 years of design and application experience. He oversees development of the company’s rugged M2M connectivity solutions for wireless and wired networks based on serial, Ethernet, wireless and USB communication technology. Fahrion has particular experience in reliable connectivity solutions for devices deployed at the “edge” of networks in remote, harsh or uncontrolled environments. He is a speaker and widely published author. He holds a BSEE from Iowa State University.