View Full Version : ControlLogix as modbus master help
September 4th, 2008, 10:20 AM
I am trying to setup a controllogix processor as a master for an accutech wireless base station. The base station has a modbus 485 connection, so I am using a 1761-NET-AIC converter to go to the processor's 232 connection. I have followed all of allen bradley instructions on setting up the processor as a modbus master. We have the baud rates on each device set accordingly. The transmission lights on the converter are all flashing, so it seems we are sending and receiving. I am just not getting a slave response in the allen bradley tags. I am also not receiving any data. I appreciate any help as I have been working on this for a few days.
November 23rd, 2008, 04:50 PM
I am also having the exact problem can anyone assist.
November 23rd, 2008, 05:49 PM
To troubleshoot Logix Modbus Master application you should try this:
- load UNMODIFIED application provided by Rockwell,
there are two places to get it: from Samples folder on your hard drive or I recommend you to get ver 2 ACD files available in TN 42662 or from Sample Code Site. I beleive v17 still uses ver 1 code.
http://samplecode.rockwellautomation.com/idc/groups/public/documents/webassets/sc_legal_info.hcst?dID=63019. Release notes for ver 2 available in Technote 55213
- download trial version of Modbus Slave application from www.modbustools.com (http://www.modbustools.com/) or use any other slave simulator software.
- set Modbus Slave to address ranges you need
- set Modbus Master commands according to the user manaual - DO Not modify any logic, it should work AS IS
If at this point it still does not work, put this project here along with ranges you are trying to read and I will check it.
Information on how to use Offset In Master available in TN 56492 but not required to start
November 23rd, 2008, 09:01 PM
I can't help you on how to solve this problem but can give you a solution. If you want to easily connect your plc to your Modbus wireless base station you could try our 451EM gateway. Adding Modbus RTU slaves is a cinch. Very simple to use.
November 24th, 2008, 11:24 AM
According to the Accutech manual at
there are two different modes of addressing. Are you using the register mapping mode?
"Note: The Base Radio provides different Device ID modes in order to support a wide range of Modbus equipment.
In the Register Mapping Mode the data for the Base Radio and all Field Units are located under a single device ID. This ID may be any allowable Modbus address between 1 and 247 that doesn’t conflict with an address of existing device or Modbus network.
In the Device ID Mapping Mode each Field Unit is given its own unique ID and registers. The Field Unit ID is equal to the value of the Base Radio ID added to the Field Units RF ID." (pg 32)
November 24th, 2008, 02:14 PM
For what it's worth. Have you tried to connect with any other Modbus Masters? I have a Shareware I downloaded from the web , it's porved that useful I intend to buy it. Search for SimlyModbus. very handy little diagnsotic