Connecting Honeywell UDC2500 via Modbus TCP/IP to Siemens S7-1500

Hello all,

Its the first time I write here so I greet everyone.
I am trying to connect a honeywell UDC2500 with the Ethernet kit to a Siemens S7-1515F-2PN PLC.
I would like to read the value (PV), which is a temperature value of an industrial oven.
To do this I use the instruction MB_Client. Configuring this instruction I am not able to receive data, I do not understand well how I have to configure the MB_Client addresses to receive data. The instruction error is 80C8. I've talked to siemens and tried to do everything, but I'm sure I'm doing something wrong.
In honeywell I have set to "COM" for (ComADR = 3) and (ComSTA = ETHR).
Do I need to connect a sensor? I have only connected the power and the ethernet connection.

I attach you some pictures...
I ask for help to get out of this problem.

Regards, and thank you very much.


I can't help you with the Siemens master, but I can tell you a sad tale about the Honeywell UDC 2500.

The Ethernet IP address can only be configured with Honeywell PIE software. There is no means to configure the IP address via the keyboard.
The default IP address for the 2500 Ethernet card is It can be changed only with PIE software.

The ComADR address is not used for Modbus over Ethernet (it's the slave node ID for RTU over RS-485).
ComSTA is configured at ETHR for Ethernet or MODB for the RS-485 card.

If you decide you want to switch to the RS-485 option card for the 2500, that uses the slave ID address setting ComADR, configurable under the COM settings, along with baud rate, but the card uses NO parity only, there is no selection ODD or EVEN (it's 8-N-1).

If you get the hardware bus operating, the PV value can be read from the Holding Register memory area with Function Code 03
- from (4)0001 as a 16 bit signed integer with an assumed single digit to the right of decimal point (PV*10).
- from (4)0065 as a 32 bit floating point value. The word/byte format is one of the two common formats, FP B, or FPLB configured under the WS FLT parameter.

The Modbus register map in the UDC 2500 manual is useless because it is used only for Function code 20/21, for which there are no commercial Masters.

The useable Honeywell Modbus manual is Modbus® RTU Serial Communications User Manual, 51-52-25-66, Revision T, February 2013

Yes, you need a valid sensor connection for whatever input type is configured. In a pinch, configure it for a thermocouple and short the input to read ambient temperature, but the absence of a valid input signal will generate an input error that will fault the Modbus communications.

As they say, Modbus is a project.