Modbus_master.ocx contains a 32-bit custom control which allows Visual Basic and other OLE Container applications to quickly and easily access data points contained in a modbus slave device connected to the PC. The modbus device may be connected directly to a PC COM port or accessed via a network connection using the modbus/TCP, communications protocol standard. Modem connections are also supported using the Win32 TAPI, (Telephony APplication Interface) library. Multiple connections may be made from the application to different COM ports and/or network devices and each connection operates independently, allowing asynchronous operation to multiple devices on multiple modbus networks.
The Modbus_Master Control exposes properties to define the physical connection, (such as BaudRate, Parity, etc.), and methods to connect to a com port, network, or TAPI device.
Each connection is identified by a unique handle returned from the control when the connection is established. The application initiates messages, (reads & writes), to a device using either the PollModbus and/or WriteModbus method. All messages are processed by the control in the background allowing the application logic to continue while the character string is formatted and transmitted to the selected device. The control processes all response messages, verifies the proper checksum and posts the SlaveResponse Event to the application detailing the results of the message transaction. Upon processing the SlaveResponse Event, the application can obtain the results of the read or write request.
Last Updated: Movember 12, 2002