Fun with Red Lion DSP – Polling MC-IIIs

The Red Lion DSP is a great little unit. It has mostly the same internals as their G3 HMI line but without the display. This makes it useful as a protocol conversion box, a data collector or a simple web based remote monitoring unit using the built-in web server. BUT it has its quirks; it doesn’t have a lot of horsepower so if you are doing a lot of web server functionality you might have trouble when you start hitting the CPU limits of the unit.

A friend recently connected with me regarding some trouble they were having trying to get the Red Lion DSP talking to a RS-485 line with several NuFlo MC-III units on it. If they tried just one unit it worked fine. But as soon as they enabled a second one (even on a different serial port!) the Red Lion could not poll either unit. What they learned is worth sharing!

Turns out you need to disable the Ping Holding Register! Weird right?! Now you know. Thanks Cory Crowe for this great tidbit of information.