JB_acg (Customer) asked a question.

January 10, 2023 at 8:51 PM
Comm errors with when communicating to a FA-ISOCON via USB-RS232 converter

Hello,

I am setting up a prototype measurement system using discrete RS485 modbus components.

 

I need to control these devices from a PC via RS-232. TO accomplish the comm path, I have USB-RS232 converter cable which then connects to AutoDir FA-ISOCON adapter. I am setup for 9600 baud/1stop/even parity in the adapter and PC; Tx Control= Auto Network Tx Enable.

 

I'm use to Modbus Poll to send/receive data. I see 'blinky' lites indicating Tx/Rx activity, and I constantly get BREAK errors on writes and Parity errors on reads.

 

I don't have any hardware/equipment to analyze activity to figure out what might be happeing on lines. I do have a SPY software port monitor.

 

I do know my 485 devices are functional (via Modbus Poll software-> USB-485 converter-> Measurement Device.

 

Has anyone successfully used a USB-232 converter to talk with FA-ISOCON? Any issues, problems? I've tried various switch settings to no avail

 

 

  • 4 answers
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  • ADC TechnologyGroup_05 (AutomationDirect)

    I just conducted a quick test and have successful communication between my Modbus client and server.

     

    Using Modbus Poll as the client device, I am connected to the RJ12 port of the FA-ISOCON using the EA-MG-PGM-CBL (USB to RS-232 converter).  

    Modbus Poll is configured for 9600 baud, 8 data bits, 1 stop bit, Even parity.

    The FA-ISOCON is configured for 9600 baud (S21=1, S22=0, S23 = 0)

    The FA-ISOCON has the 'Terminate", '0V Bias', and '5V Bias' dipswitches set to ON.

    The FA-ISOCON has the two '1/2 DPX' dipswitches set to ON.

     

    Because the '1/2 DPX' dipswitches are both set to ON, I do not need to jumper the RXD+ to TXD+ and the RXD- to TXD-. Therefore, I have the FA-ISOCON TXD+ terminal wired to the D+ terminal of my Do-More BRX serial port and the FA-ISOCON TXD- terminal wired to D- terminal of the Do-More BRX serial port.  

    Both Reads (Function Code 3) and Writes (Function Code 16) are working as expected and exchanging data between the client and server.

     

    The BRX is configured as a Modbus RTU server with 9600 baud, 8 data bits, 1 stop bit, and Even parity.

     

    If possible, I would try to eliminate your USB to RS-232 converter as a suspect and use a client that can support RS-232 without conversion. My circumstances allow me to use Do-More, Click, and Productivity CPUs for this.

     

    I hope this helps.

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  • ADC TechnologyGroup_05 (AutomationDirect)

    I just conducted a quick test and have successful communication between my Modbus client and server.

     

    Using Modbus Poll as the client device, I am connected to the RJ12 port of the FA-ISOCON using the EA-MG-PGM-CBL (USB to RS-232 converter).  

    Modbus Poll is configured for 9600 baud, 8 data bits, 1 stop bit, Even parity.

    The FA-ISOCON is configured for 9600 baud (S21=1, S22=0, S23 = 0)

    The FA-ISOCON has the 'Terminate", '0V Bias', and '5V Bias' dipswitches set to ON.

    The FA-ISOCON has the two '1/2 DPX' dipswitches set to ON.

     

    Because the '1/2 DPX' dipswitches are both set to ON, I do not need to jumper the RXD+ to TXD+ and the RXD- to TXD-. Therefore, I have the FA-ISOCON TXD+ terminal wired to the D+ terminal of my Do-More BRX serial port and the FA-ISOCON TXD- terminal wired to D- terminal of the Do-More BRX serial port.  

    Both Reads (Function Code 3) and Writes (Function Code 16) are working as expected and exchanging data between the client and server.

     

    The BRX is configured as a Modbus RTU server with 9600 baud, 8 data bits, 1 stop bit, and Even parity.

     

    If possible, I would try to eliminate your USB to RS-232 converter as a suspect and use a client that can support RS-232 without conversion. My circumstances allow me to use Do-More, Click, and Productivity CPUs for this.

     

    I hope this helps.

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    Selected as Best

  • JB_acg (Customer)

    Thank you for the testing information.

    I just tried the test using the EA-MG-PGM-CBL converter cable and DIP settings that you used. Based on Tx/Rx lites on each device and polling at slow rate, things look good, but Modbus Poll reports Write error / Read Error: Framing Error.

     

    Next, will disconnect the USB/232 converter and try direct PC/232 port to FA-ISOCON serial port connections.

  • JB_acg (Customer)

    I am now successfully communicating with my devices via the FA-ISOCON using either the EA-MG-PGM-CBL converter cable or directly from the PC RS-232 port.

     

    A couple of things to note:

    1. The following switch settings are used/needed on the FA-ISOCON: TERMINATE, 1/2DPX / 1/2 DPX; the 5V/0V switches had no observable effect. on or off
    2. My driver for the EA-MG-PGM-CBL was likely out of date on my Win10 PC; after updating, things began to work.
    3. I did notice when I was getting comm errors, the TXD EN was always on/stuck.

     

    For now, problem appears resolved. Thanks for the assist.

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