Siemens SIMATIC S7 System Manual page 482

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9.3 Modbus RTU library

Parameter Parity is set to match the parity of the Modbus slave device. All settings use one

start bit and one stop bit. The allowed values are: 0 (no parity). 1 (odd parity), and 2 (even

Parameter Port sets the physical communication port (0 = RS-485 integrated in CPU, 1 =

RS-485 or RS-232 located on the optional CM01 signal board).

Parameter Timeout is set to the number of milliseconds to wait for the response from the

slave. The Timeout value can be set anywhere in the range of 1 millisecond to 32767

milliseconds. A typical value would be 1000 milliseconds (1 second). The Timeout parameter

should be set to a value large enough so that the slave device has time to respond at the

selected baud rate.

The Timeout parameter is used to determine if the Modbus slave device is responding to a

request. The Timeout value determines how long the Modbus Master will wait for the first

character of the response after the last character of the request has been sent. The Modbus

master will receive the entire response from the Modbus slave device if at least one

character of the response is received within the Timeout time.

When the MBUS_CTRL / MB_CTRL2 instruction completes, the instruction returns TRUE for

the Done output.

The Error output contains the result of executing the instruction.

See also Modbus RTU master execution error codes (Page 487)

System Manual, V2.3, 07/2017, A5E03822230-AF

S7-200 SMART

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