Control.com - Nerds in Control

I have this problem:

I try to setup a comunication between a modbus master simulator (www.modbustools.com) and a real ABB PLC slave (this PLC use the comunication modbus interface CI867).

When the master send a request (for example 03 Read Holding Registers) the PLC respondes with an exception: "04 Illegal Response Length". I try with other function codes and it's the same and I try with another simulator (Triangle MicroWorks) and it's the same...

Anyone have suggestions to solve this problem ?

Hi there,

Are you sure that the exception, 04, is Illegal Response Length. The modbus spec. says that 04 is: An unrecoverable error occurred while the slave was attempting to perform the requested action.

/Pat

That Exception is sometimes called "Illegal Response Length" and sometimes "Slave Device Failure". Anyway I'm near to solve the problem, but ABB documentation is very confusing. Now I try to configure the communication interface for modbus and there are some function block like MBConnect, MBRead ext anyone knows this function?

Quoting from the ABB Control Builder M On-Line Help Documentation ......

Usage of ModBus

ModBus can be used for Point-to-Point or Multidrop communication. Communication takes place serially and asynchronously, based on the Master/Slave principle, and in half duplex.

Controllers only support master communication.