FB_MBReadWriteRegs (Modbus-Funktion 23)

This function first reads 1 to 128 output registers (16 bit) and then writes 1 to 128 output registers (16 bit).

Inputs

VAR_INPUT
    sIPAddr       : STRING(15);
    nTCPPort      : UINT:= MODBUS_TCP_PORT;
    nUnitID       : BYTE:=16#FF;
    nReadQuantity : WORD;
    nMBReadAddr   : WORD;
    nWriteQuantity: WORD;
    nMBWriteAddr  : WORD;
    cbDestLength  : UDINT;
    pDestAddr     : POINTER TO BYTE;
    cbSrcLength   : UDINT;
    pSrcAddr      : POINTER TO BYTE;
    bExecute      : BOOL;
    tTimeout      : TIME;
END_VAR

Name	Type	Description
sIPAddr	STRING (15)	Is a string containing the IP address of the target device.
nTCPPort	UINT	Port number of the target device.
nUnitID	BYTE	Identification number of a serial sub-network device. If a device is addressed directly via TCP/IP, this value must be 16#FF.
nReadQuantity	WORD	Number of output registers (data words) to be read. The value zero is not permitted.
nMBReadAddr	WORD	Start address of the output registers to be read (word offset).
nWriteQuantity	WORD	Number of output registers (data words) to be written. The value zero is not permitted.
nMBWriteAddr	WORD	Start address of the output registers to be written (word offset).
cbDestLength	UDINT	Contains the maximum byte size available in the destination buffer for the register values to be read. The buffer must have at least the byte size: nReadQuantity 2*.
pDestAddr	POINTER TO BYTE	Contains the address of the destination buffer into which the data are to be read. The buffer can be a single variable, an array or a structure, whose address can be determined with the ADR operator.
cbSrcLength	UDINT	Contains the maximum available byte size of the source buffer that contains the register values to be written. The buffer must have at least the byte size: nQuantity 2*.
pSrcAddr	POINTER TO BYTE	Contains the address of the source buffer that contains the data to be written. The buffer can be a single variable, an array or a structure, whose address can be determined with the ADR operator.
bExecute	BOOL	The function block is enabled by a rising edge at this input.
tTimeout	TIME	States the length of the timeout that may not be exceeded by execution of the ADS command.

Outputs

VAR_OUTPUT
    bBUSY      : BOOL;
    bError     : BOOL;
    nErrId     : UDINT;
    cbRead     : UDINT;
END_VAR

Name	Type	Description
bBusy	BOOL	When the function block is enabled, this output is set and remains set until a feedback is received.
bError	BOOL	If an ADS error should occur during the transfer of the command, then this output is set once the bBusy output is reset.
nErrId	UDINT	Returns the ADS error number when the bError output is set.
cbRead	UDINT	Contains the number of bytes currently read.

Sample of calling the function block in FBD

PROGRAM Test
VAR
    fbReadWriteRegs          : FB_MBReadWriteRegs;
    bReadWriteRegs           : BOOL;
    bReadWriteRegsBusy       : BOOL;
    bReadWriteRegsError      : BOOL;
    nReadWriteRegsErrorId    : UDINT;
    nReadWriteRegsCount      : UDINT;
    nRdQuantity              : WORD;
    nRdMBAddr                : WORD;
    nWrQuantity              : WORD;
    nWrMBAddr                : WORD;
    arrRdData                : ARRAY [1..9] OF WORD;
    arrWrData                : ARRAY [1..9] OF WORD;
END_VAR

FB_MBReadWriteRegs (Modbus-Funktion 23) 4:

After a rising edge of "bExecute" and successful execution of the ReadWriteRegs command, arrRdData contains the read register data, and the data from arrWrData are written to the registers.

Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT v3.1.0	IPC or CX (x86, x64, ARM^®)	Tc2_ModbusSrv