Siemens SIMATIC S7 Manual page 38

DONE_NDR
ERROR
STATUS
STATUS_FUNC
IDENT_CODE
UNIT
OPEN MODBUS / TCP communication via CP343-1 and 443-1
2XV9450-1MB00; Manual edition 4.3
In the operating mode "CP is client" the activated request was executed
without error. For a read function the response data from the server has
already been entered into the DB. For a write function the response to the
request telegram has been received from the server.
In the operating mode "CP is server" this output indicates a telegram
exchange without errors. In the parameters UNIT, DATA_TYPE,
START_ADDRESS, LENGTH and WRITE_READ the request parameters of
the client are displayed. These outputs are only available and valid as long as
DONE_NDR is TRUE.
When this output is set, an error was recognized.
In the operating mode "CP is client" the activated request was ended with an
error. The error number is displayed in the STATUS output.
In the operating mode "CP is server" an error is detected at a request
telegram of the client or at sending a response telegram. The error number is
displayed in the STATUS output.
The STATUS output displays the error number when ERROR is TRUE. The
error numbers are described in chapter 6.
This parameter shows the name of the function, which caused the error
occurred.
After start-up of the PLC this parameter displays the identification code, an 18
character string. With this IDENT_CODE you can order the registration key at
IT4industry.
You can find further information in section "Licensing".
In mode "CP is client" the parameter UNIT is an input parameter. This input
has to be set according to the requirements. The FB copies this value to the
request telegram and verifies when the respond telegram is received.
In mode "CP is server" the parameter UNIT is an output parameter. The FB
copies this value from the request telegram to the respond telegram. The
output is set with the received value when the job is finished without error.
Function Block MODBUSCP
5-10