Судя по этим объвялениям
Код:
Public Declare Function mytext Lib "ModbusRTU.dll" _
(ByRef Arr As Byte, ByRef mn As Integer) As Boolean
Public Declare Function ModRTU_CRC Lib "ModbusRTU.dll" _
(ByRef Arr As Byte, ByVal n As Long) As Long
Public Declare Function openPort Lib "ModbusRTU.dll" _
(ByVal NPort As String, ByVal Speed As Long, ByVal parity As Long, _
ByVal StopBits As Long, ByRef NPort As Long) As Boolean
Public Declare Function closePort Lib "ModbusRTU.dll" _
(ByVal NPort As Long) As Long
Public Declare Function WritePort Lib "ModbusRTU.dll" _
(ByVal NPort As Long, ByRef Arr As Byte, ByVal n As Long) As Long
Public Declare Function ReadPort Lib "ModbusRTU.dll" _
(ByVal NPort As Long, ByRef Arr As Byte, ByVal n As Long) As Long
Public Declare Function ieee754 Lib "ModbusRTU.dll" _
(ByRef Arr As Byte) As Single
Public Declare Function ieee754inv Lib "ModbusRTU.dll" _
(ByRef Arr As Byte) As Single
Public Declare Sub float32ToBuffer Lib "ModbusRTU.dll" _
(ByRef Arr As Byte, ByVal Num As Single)
Тут все объявления как __stdcall сделаны
А значит можно из любых языков использовать