Good Morning,
First off, let me apologize as I'm totally out of my element on this topic. I'm mostly a metallurgist and this communications stuff is above my head. Hopefully I've got this in the right forum for some help.

I've got a furnace that uses an older obsolete Honeywell UDC5000 controller. This controller was set up to talk to the rest of the Furnace/PLC/Computer with RS485 ASCII (as far as I can tell from the Honeywell documentation of the UDC5000). This controller is broken and I need to replace it with a UDC3500 as this is the replacement model. My problem is that the UDC3500 communicates with Modbus RTU and as far as I can tell that's not compatible with the ASCII set-up the old controller had.

Anyone know of a way to get the new Modbus RTU controller into the ASCII network?


I've found a product that may work (http://www.rtaautomation.com/products/460/mma.html) but I don't really know for sure. As I've mentioned, I'm just fumbling my way through this subject so I don't know if what I've found will work or is for another application entirely.

Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast

Modbus (over serial line) comes in two favors: RTU and ASCII. Same protocol however the way data is represented as characters is different. Now it is possible that the old controller was talking a completely different protocol then Modbus ASCII. Prosoft Technology makes a variety of protocol gateways that will probably solve your problem.

The UDC 5000's ASCII and DMCS communications protocols were both proprietary protocols. To my knowledge there is no commercial protocol converter for either.

There are devices like Red Lion's Data Station that can read the Modbus registers from a UDC3500 and then be programmed to provide the data on another communications port, but implementation requires custom programming. You'd probably have to hire a 'system integrator' (a process SI guy, not an IT SI guy) to accomplish that, someone already familiar with Modbus.

The UDC 5000 was an early '90's product in a period when the market was sorting out communications protocols. Most of the proprietary protocols lost the war. Modbus won. It survived and thrives.

It isn't clear what your ASCII network consists of, but you should be aware that most HMI software packages nowadays read, display and historize data from process instruments routinely talk Modbus.