Chromalox Modbus


Thread Starter


When will the world realize that there are different types of MODBUS. Chromalox say it is modbus compatible. That's great, what type?

Has anyone had any luck talking to a chromalox panel, if so how did it work? Thanks.
By revealing only that you've got a Chromalux panel, you've mimicked exactly what Chromalux has done to you: Chromalux assumes you know which flavor of Modbus they're talking about, and you assume we know what a Chromalux panel is. Who's on first?

In the absence of knowing any more about Chromalux than they used to make heaters, I'll give you my Modbus overview:

Modbus Plus is proprietary and generally only found on Schneider and associated companies' controls and being proprietary those using it know because they've paid dearly for its licensing and multiple master capability.

Modbus RTU is everywhere and runs on RS-232 or RS-485, occasionally RS-422. Since it is license free, it is very widely used. Modbus RTU is, by definition, 8 bit data words.

Modbus ASCII is used less and less over time. It requires transmitting twice the number of characters for the same data, and has fallen out of favor over the years, although I've encountered some single loop temperature controllers that use Modbus ASCII without calling it Modbus ASCII. Modbus ASCII is, by definition, 7 bit data words.

The data word size is always specified in the device's documentation somewhere in the documentation for the serial port. Well, almost always.

Modbus TCP is Modbus over ethernet.

Daniels and Enron versions of Modbus are used for flowmetering, and the documentation would reflect such.

So, if you haven't paid for Modbus Plus and have no license for it, you probably don't have it.

Unless Chromalux has expanded into flow meters you probably will not have to deal with the Daniels or Enron versions.

If the data word is 8 bits, you have Modbus RTU.

If the data word is 7 bits, you are dealing with Modbus ASCII.

If the Modbus port is an ethernet port, you have Modbus TCP.

Chances are if the "panel's" Modbus port is an RS-485 port, it's Modbus RTU, if it's an ethernet port, you are dealing with Modbus TCP.

Your next frustration will probably be why the data formats aren't defined (it's just assumed you know it's signed integer. Just joking, I have no idea what it is)

Once slight addition to this explanation is that some manufacturers add a third party serial to Ethernet converter to their products as an option to tunnel Modbus/RTU over Ethernet. This is sometimes described as "Modbus over Ethernet", but it's really Modbus/RTU and <i>not</i> Modbus/TCP.