Entry type: FAQ, Entry ID: 58378388, Entry date: 02/29/2012

Why is the value A083 (hex) output permanently at the STATUS output parameter of the block for Modbus TCP when the ENQ_ENR=true input parameter has been set?

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  • Associated product(s)

The products below with the corresponding Modbus blocks are available for Modbus communication with the SIMATIC S7.

Product Modbus block
Modbus TCP CP FB108
Modbus TCP Redundant FB1733
Modbus TCP Redundant V2 FB909, FB907
Modbus TCP PN CPU FB102

You call the relevant Modbus block in the user program of the CPU.
You set the ENQ_ENR=true input parameter and the value A083 (hex) is permanently at the STATUS output parameter of the Modbus block.

The value A083 (hex) at the STATUS output parameter means that a new Modbus message has been triggered with the input parameter ENQ=true or ENQ_ENR=true, although the previous task is still running.

Below we describe the causes of the status value A083 (hex) and the remedies you can apply.

  • The value A083 (hex) only occurs at the STATUS output parameter when the Modbus block has been parameterized as client. If the status value A083 (hex) is output even though the S7 CPU is supposed to be working as server, then you must correct the parameterization of the Modbus block in OB100.
  • Triggered Modbus messages are always terminated with DONE / DONE_NDR or ERROR. No new message may be triggered while a message is being processed.
  • If the server for the S7 CPU is no longer accessible while a Modbus job is running, the status value A083 (hex) might be present after reconnection. In this case, insert the line below when setting ENQ_ENR:


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