Ajay Garg

Newbie questions regarding reading data from 1766-L32BWA

3 posts in this topic

Hi All.

We have the Micrologix-1400 1766-L32BWA PLC, and we are in process of understanding how to read data from it using our custom, simple, external application in a high-level language (C in our case).

Following is what we have achieved so far :

  • Been able to connect the PLC with a laptop, and able to browse (via the PLC's embedded web-server) over PLC's-IP
  • The PLC is pre-programmed, and have the (default) program-files and data-files (picture PLC-files.png attached).
  • Also, some data is shown (eg. N7-Data-File.png attached).

Also, we have following strict limitations :

  • Nothing is to be changed inside the PLC, so any (ladder-logic) programming inside the PLC is out of the question.
  • The only external interface available to us is the Ethernet (physical) interface. None of RS232, RS485 is available to us.

Now, for simplicity, let's say we want to read just the values in N7 data file (using our custom, simple, external application in a high-level language). Since 1766-L32BWA is a A-series PLC, so I guess Modbus-TCP is out of the question.

So, what would be the best way to read data from N7 data file via Ethernet (physical) interface. Ideally, we would want that our external application fires a command, and receives the appropriate response from the PLC. We have been reading that Ethernet/IP could be an option, but have been unable to find any concrete Request/Response example (of Ethernet/IP packet). 


I am sorry if I sound too noob.

Hoping to get some help from the experts ...


Thanks and Regards,




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You make two statements that contradict each other.  "Nothing is to be changed inside the PLC" and "external application fires a command".  Data collector instructs PLC to provide data means the PLC will need to see a command from the data collector, which will require a PLC tag and some logic.

Is the data collection to be time-driven (i.e., every X units of time, send Y blocks of data) or event-driven (i.e., datapoint Z has changed within a range, send Z datapoint).

Is handshaking required to insure the data was captured (i.e., are alarms needed to alert that data was not captured, that the system is not functioning)?

There are 3rd party tools for utilizing Ethernet/IP to obtain data from a Logix PLC.  RTA has a product for such.  https://www.rtaautomation.com/software-solutions/ethernetip-client-tagc


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You might want to look at AdvancedHMI to get information out of your PLC. This is a free software that can downloaded at the following URL:

It already has the Allen Bradley Ethernet/IP Driver written for SLC,MicroLogix, PLC5, ControlLogix, and CompactLogix. AdvancedHMI was written in VB.Net and runs on Visual Studio. This means you can use your C programming within visual studio.

Here is some more information on AdvancedHMI and the AB Ethernet IP driver:

Hope this helps you out.

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