Parameters - Manual - SIMATIC AX - Instructions that can be used for Modbus-RTU communication. - Siemens.Simatic.S71500.CommunicationsProcessor.ModbusRtu,library

Name	Type	Section	Description
request	BOOL	Input	Activates configuration of the port on rising edge
port	WORD	Input	Communication port, Hardware Identifier
baud	UINT	Input	Selection of the data transmission rate. Valid values are: 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 76800, 115200 bit/s.
parity	UINT	Input	Selection of parity: 0 - None 1 - Odd 2 - Even
flowControl	UINT	Input	Selection of flow control: 0 – (default) no flow control 1 – Hardware flow control with RTS always ON (not with RS422/485 CMs) 2 – Hardware flow control with RTS switched (not with RS422/485 CMs)
rtsOnDelay	UINT	Input	Selection RTS ON delay: 0 – No delay from "RTS active" until the first character of the frame is sent. 1 to 65535 – Delay in milliseconds from "RTS active" until the first character of the frame is sent (not with RS422/485 CMs). RTS delays must be used independent of the selection FLOW_CTRL.
rtsOffDelay	UINT	Input	Selection RTS OFF delay: 0 – No delay after transmission of last character until "RTS inactive" 1 to 65535 – Delay in milliseconds after transmission of last character until "RTS inactive" (not with RS422/485 ports). RTS delays must be used independent of the selection FLOW_CTRL.
responseTimeout	UINT	Input	Response timeout: 5 ms to 65535 ms - Time in milliseconds that ModbusMaster waits for a response from the slave.
MB_DB	P2P_MB_BASE	Input/Output	A reference to the instance data struct of the ModbusMaster or ModbusSlave instructions.
done	BOOL	Output	TRUE, if the instruction finished without error
error	BOOL	Output	TRUE, for one cycle once the instruction has been completed with an error.
status	WORD	Output	Error code. See Parameter Status.

ModbusCommonLoad is executed to configure a port for the Modbus RTU protocol. Once you have configured the port for the Modbus RTU protocol, it can only be used by the ModbusMaster or ModbusSlave instructions.

You have to run ModbusCommonLoad for the configuration of each communication port that is to be used for Modbus communication. You must assign a unique ModbusCommonLoad instance to each port that you use. Only run ModbusCommonLoad again if you need to change communication parameters, such as data transmission rate or parity, or in case the network has returned.

For example, an instance is assigned to the instruction if you add ModbusMaster or ModbusSlave to your program. You need to connect the MB_DB parameter of the ModbusCommonLoad instruction to the MB_DB parameter of the ModbusMaster or ModbusSlave instruction.