FB_MBDiagnose (Modbus function 8)

The diagnosis function provides a series of tests for checking the communication system between the master and the slave and for examining a variety of internal error states within the slave.

Inputs

VAR_INPUT
    sIPAddr       : STRING(15);
    nTCPPort      : UINT:= MODBUS_TCP_PORT;
    nUnitID       : BYTE:=16#FF;
    nSubFnc       : WORD;
    nWriteData    : WORD;
    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.
nSubFnc	WORD	The sub-function to be executed.
nWriteData	WORD	The data word to be written.
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;
    nReadData  : WORD;
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.
nReadData	WORD	Supplies the read data word.

Sample of calling the function block in FBD

PROGRAM Test
VAR
    fbDiagnose          : FB_MBDiagnose;
    bDiagnose           : BOOL;
    bDiagnoseBusy       : BOOL;
    bDiagnoseError      : BOOL;
    nDiagnoseErrorId    : UDINT;
    nSubFnc             : WORD;
    nReadData           : WORD;
    nWriteData          : WORD;
END_VAR

After rising edge of "bExecute" and successful execution of the diagnostic command, nReadData contains the read data word.

Requirements

Development environment	Target system type	PLC libraries to be linked
TwinCAT v3.0.0	PC or CX (x86)	Tc2_ModbusSrv