Bit 000007 (Customer) asked a question.

Edited October 13, 2023 at 10:22 PM
How many click slaves per one click master?

Hello, so I currently have 5 click PLCs using modbus TCP via WLAN. 4 of them are slaves 1 is the master. Im using the master click to **recieve** counts from the slave plcs for part counts from stamping presses around a plant. The master plc is then showing all those counts on a EA9 HMI. I was wondering how many slave PLCs a master can keep receiving from, is there a limit? I was planning on adding 10 more.

thanks

Edit: This is a pretty new project I’m working on so I’d like to also add that every other day all the slave PLCs counts have been freezing on the master PLC until I cycle power to the master PLC then everything goes back to normal. Is this a wifi issue?

  • 6 answers
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  • ADC TechnologyGroup_01 (AutomationDirect)

    I'd like to clarify two points.

     

    These limits are for simultaneous active connections. You may have as many TCP Slave (Server) devices as needed. But at any point in time you may only have Send/Receive Instructions Enabled for 4 devices. The PLC will close an unused connection to one device, and then open a new connection to another device. In this way you can use ladder code to control the update rates and priority of each ModbusTCP Server device.

     

    Since you are using WLAN. The Port1 and WLAN connection limits are independent for ModbusTCP. So 4 connections for Port1, and separately 4 connections for WLAN.

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    • HOST_franji1 (HOST Engineering)

      Those Slave IDs are for Modbus/RTU devices hanging off a Modbus/TCP Gateway.

       

      Usually, each Modbus/TCP slave device has their own unique IP Address, and the Slave ID is fixed at 255 (sometimes 1).

      • Todd Dice (Customer)

        Oops, that makes sense as it's separate from IP address. I took a cursory look in the manual and could not find an answer in the Communications chapter for maximum amount of slaves.

         

        Regarding his edit question; would it make sense to have a condition that goes false once a day that is enabling the Receive so cycling power to the master isn't necessary?

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  • ADC TechnologyGroup_01 (AutomationDirect)

    I'd like to clarify two points.

     

    These limits are for simultaneous active connections. You may have as many TCP Slave (Server) devices as needed. But at any point in time you may only have Send/Receive Instructions Enabled for 4 devices. The PLC will close an unused connection to one device, and then open a new connection to another device. In this way you can use ladder code to control the update rates and priority of each ModbusTCP Server device.

     

    Since you are using WLAN. The Port1 and WLAN connection limits are independent for ModbusTCP. So 4 connections for Port1, and separately 4 connections for WLAN.

    Expand Post
    Selected as Best

    • Bit 000007 (Customer)

      Thank you very much for the detailed response.

 

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