FB_MBDiagnose (Modbus function 8)

FB_MBDiagnose (Modbus function 8) 1:

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.

VAR_INPUT

VAR_INPUT
    sIPAddr      : STRING(15);
    nTCPPort     : UINT:= MODBUS_TCP_PORT;
    nUnitID      : BYTE:=16#FF;
    nSubFnc      : WORD;
    nWriteData   : WORD;
    bExecute     : BOOL;
    tTimeout     : TIME;
END_VAR

sIPAddr : Is a string containing the IP address of the target device.

nTCPPort : Port number of the target device.

nUnitID: Identification number of a serial sub-network device. If a device is addressed directly via TCP/IP, this value must be 16#FF.

nSubFnc : The sub-function to be executed.

nWriteData: The data word to be written.

bExecute: The function block is activated by a rising edge at this input.

tTimeout: States the length of the timeout that may not be exceeded by execution of the ADS command.

VAR_OUTPUT

VAR_OUTPUT
    bBusy       : BOOL;
    bError      : BOOL;
    nErrId      : UDINT;
    nReadData   : WORD;
END_VAR

bBusy : When the function block is activated this output is set. It remains set until an acknowledgement is received.

bError : If an ADS error should occur during the transfer of the command, then this output is set once the bBusy output is reset.

nErrId : Supplies the ADS error number when the bError output is set.

nReadData: Supplies the read data word.

Function specific ADS error code

Possible reason

0x8001

Modbus function not implemented

0x8002

Invalid address or length

0x8003

Invalid parameters: - wrong number of registers

0x8004

Modbus server error

Example of calling the 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

FB_MBDiagnose (Modbus function 8) 2:

After rising edge of "bExecute" and successful execution of the diagnosis 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