FB_WriteReadVar: Write and Read Function Block

Overview

The function block FB_WriteReadVar can be used to:

owrite consecutive internal registers and read back their values in the same execution cycle of the function block (single transaction),

owrite consecutive internal registers and read different registers.

The following graphic shows the pin diagram of the function block FB_WriteReadVar:

The function block FB_WriteReadVar reads and writes internal registers (MW type only) to an external device in the Modbus protocol. The read and write operations are contained in a single transaction. Note that the write operation is performed first.

I/O Variables Description

The table describes the input variables of the function block in the TwidoEmulationSupport library:

Input	Data type	Description
i_xExecute	BOOL	The function is executed on the rising edge of this input. NOTE: When i_xExecute is set to TRUE at the first task cycle in RUNNING after a cold or warm reset, the rising edge is not detected.
i_xAbort	BOOL	Stops the ongoing operation at the rising edge.
i_iLink	INT	Indicates the port used to communicate. o1 = Serial port 1 o2 = Serial port 2 o3 = Ethernet / Modbus TCP
i_iId	INT	Device identifier of targeted external device: oSerial line slave address: 1...247 or oEthernet index: 1...16 (Depends on the link configuration).
i_iTimeout	INT	Set the maximum time to wait to receive a response from the modem. Specified in ms. A value of 0 means no timeout is enforced.
i_diFirstReadObj	DINT	Address of the first object from which values are read.
i_iReadQuantity	INT	Number of objects to read.
i_pbyReadBuffer	POINTER TO BYTE	Address of the buffer in which read object values are stored.
i_diFirstWriteObj	DINT	Address of the first object from which values are written.
i_iWriteQuantity	INT	Number of objects to write.
i_pbyWriteBuffer	POINTER TO BYTE	Address of the buffer in which object values to write are stored.
i_astRemoteDevices	ARRAY [1..Gc_uiRemoteAddressTableLen] OF ST_RemoteDevice	Contains the list of remote device addresses for Modbus TCP communication.

The table describes the output variables of the function block in the TwidoEmulationSupport library:

Output	Data type	Description
q_xDone	BOOL	q_xDone is set to TRUE when the function is completed successfully.
q_xBusy	BOOL	q_xBusy is set to TRUE while the function is ongoing.
q_xAborted	BOOL	q_xAborted is set to TRUE when the function is stopped with the i_xAbort input.
q_xError	BOOL	q_xError is set to TRUE when the function stops because of a detected error.
q_etCommError	SEN.CommunicationErrorCodes	q_etCommError contains the value of communication error codes SEN.CommunicationErrorCodes.
q_etOperError	SEN.OperationErrorCodes	q_etOperError contains the value of operation error codes SEN.OperationErrorCodes.