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RS-485 How to

fblanchardfblanchard
edited March 2018 in PLCnext Technology & PLCnext Controls

Hi,

I want my PLCnext to communicate with a device using our custom protocol over a legacy RS-485 link.

We plan to use the  "2688666 : AXL F RS UNI 1H" serial communication module to this end.

The only documentation I found is this document  "Communication of the AXL F RS UNI 1H via Modbus/RTU" (application note 105572_en_02), and the corresponding PLCnext libray component port definitions.

My goal is NOT to use the Modbus/RTU protocol, BUT to use our own custom one. 

-- Is it possible to do it with this hardware and component ?  It feel strange not to have a ports like 'Send' or 'Busy' to control the communication.  It's suggest that the device will transmit the frame continuously, unless there some hidden control mechanism that internally detect when the data ports are updated ....

-- Do I absolutely need to use the AXL_ComSerial_1.pcwlx  management component library ?

-- Where is the documentation ?

Thanks

Frédéric

Comments

  • Martin [PLCnext Technology Team]Martin [PLCnext Technology Team]

    Hello Frédéric,

    -- Is it possible to do it with this hardware and component ?

    Yes!

    -- Do I absolutely need to use the AXL_ComSerial_1.pcwlx  management component library ?

    No.

    -- Where is the documentation ?

    On the Phoenix Contact website:

    www.phoenixcontact.com/ie/products/2688666

    (click on the "Downloads" tab under the product picture. The document you want is the "Data Sheet" - I've also attached it below).

    -- It feel strange not to have a ports like 'Send' or 'Busy' to control the communication.  It's suggest that the device will transmit the frame continuously, unless there some hidden control mechanism that internally detect when the data ports are updated ....

    The send and receive control is described in the Data Sheet - for example, on Page 16 in the "Command Toggling" section, you can see that the characters in the transmit buffer will be sent once, when the Command is set to 001, but the same transmit characters can be sent again by toggling the Command between 101 and 001.

    The PC WORX libraries are intended to make comms easier by wrapping the raw Process Data in a more user-friendly interface, but you can manipulate the Process Data directly based on the specifications in the Data Sheet.

    Hope this helps.

    - Martin.

     

  • fblanchardfblanchard

    Thanks Martin!

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