32Bit Modbus Register and OPC Server


Thread Starter

Rashid Ashraf

I am trying to read data from FMC's Flow Management Computer using Modbus Ethernet Interface.

The issue is that FMC is using 32Bit registers for Modbus implementation. Float32 is consuming One register as opposed to Two (as per Modbus standards).

I am using TOP OPC Server for extracting data which is giving me errors "Bad received length". TOP OPCServer support says that it is receiving 4 bytes of data when requesting 2 bytes.

Any help to resolve this issue would be appreciated.


That sounds like Enron MODBUS. MODBUS does not define a 32 bit register size much less a floating point data type.

PeakHMI supports ENRON MODBUS. Use the demo installer to verify the data is correct and then you can choose which product to use.

FYI, PeakHMI has a built in OPC DA server.

Good luck,

I am already using TOP OPC Server for Modbus. It has drivers for Modbus RTU, ASCII and Ethernet.


Fred Loveless

That is Enron Modbus. Depending upon the version of TopServer you are running it will have an Enron Modbus driver in it or, the serial driver has an Omni Flow model which does Enron Modbus. The serial driver supports Ethernet Encapsulation and has a setting to enable Modbus Ethernet Headers and Footers.