MODBUS External Device

IEC variable address range

The following table lists the equipment variable address range if you have selected the IEC61131 Syntax

^*1You can set the data storing order in 32-bit data word units and 64-bit data double-word units in the Device Setting dialog box.

^*2Write disable

^*3For input addresses, such as %Ir.m.c, %IWr.m.c, or %IWr.m.c:Xj, with a minimum of two and a maximum of three segments. Each segment identifies a physical rack, module, and channel as necessary, for the associated I/O.

^*4For output addresses, such as %Qr.m.c, %QWr.m.c, or %QWr.m.c:Xj, with a minimum of two and a maximum of three segments. Each segment identifies a physical rack, module,  and channel as necessary, for the associated I/O.

^*5Read/Write, depending on the bit/word number.

^*6To fit with equipment variable coding, the most significant byte could be chosen by the software.

Non IEC variable address range

The following table lists the equipment variable address range if you haven’t selected the IEC 61131 Syntax.

^*1You can set the data storing order in 32-bit data word units and 64-bit data double-word units in the Device Setting dialog box.

^*2Write disable

^*3When you write to the bit address, the Display reads the entire word, sets the defined bit, then returns the new word value to the External Device. If the ladder program writes data to this word address during the bit write process, the resulting data may be incorrect.

IEC equivalents

The following table gives the equivalents between the Modbus syntax and the IEC61131 syntax.

^*1Leading zeros "00001" must be preserved.

^*2j is a bit index with the following convention: 0 for the least significant bit and 15 for the most significant bit.

^*3k is equal to 65535 - string length / 2 rounded to the upper value. For instance with a 11 characters string we’ve got 65535 - 6 = 65529.

IEC61131 Syntax Address Mapping

Address mapping in BLUE is as follows. %MD and %MF use two sequential words form the specified address. The %KW, %KD, and %KF are mapped similarly.

Symbol Specification

You can import symbol data from the project created by your programming software.

*1 <SYMNAME>: When referring to structures, the Symbol Name includes the structure name. The maximum number of characters for the Symbol Name is 255, which includes delimiters and elements.
Example)
    BOOL type single symbol    "BOOLSYMBOL"
    BOOL type 1D Array    "BOOL1D[10]
    WORD type 2D Array    "WORD2D[10,10]
    UDINT type 3D Array    "UDINT3D[0,1,2]
    STRING in User Defined Structure [STRUCT001]    "STRUCT001.STRINGSYM"

*2 The number of elements for each dimension is shown from "l" (the first number of the elements) to "h" (the last number of elements).