FB_MBReadCoils (Modbus function 1)

VAR_INPUT

VAR_INPUT
    sIPAddr   : STRING(15);
    nTCPPort  : UINT:= MODBUS_TCP_PORT;
    nUnitID   : BYTE:=16#FF;
    nQuantity : WORD;
    nMBAddr   : WORD;
    cbLength  : UDINT;
    pDestAddr : POINTER OF BYTE;
    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.

nQuantity : Number of digital inputs (data bits) to be read. The value of nQuantity must be > 0.

nMBAddr : Start address of the digital inputs to be read (bit offset).

cbLength : Contains the max. byte size of the destination buffer into which the data are to be read. The minimum buffer byte size must be: (nQuantity + 7) / 8.

pDestAddr : 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 found with the ADR operator.

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;
    cbRead     : UDINT;
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.

cbRead: Contains the number of bytes currently read.

Example of calling the block in FBD:

PROGRAM Test
VAR
    fbReadCoils       : FB_MBReadCoils;
    bReadCoils        : BOOL;
    bReadCoilsBusy    : BOOL;
    bReadCoilsError   : BOOL;
    nReadCoilsErrorId : UDINT;
    nReadCoilsCount   : UDINT;
    nQuantity         : WORD := 10;
    nMBAddr           : WORD := 5;
    arrData           : ARRAY [1..2] OF BYTE;
END_VAR
 

After a rising edge of "bExecute" and successful execution of the ReadCoils command, the content of digital outputs 6 - 15 is written into the arrData array:

Requirements