Connect21 – application for working with Modbus industrial protocol, widely used in industry as well as in building automation. Connect21 enables connection to various Modbus slaves, such as sensors, PLCs, servers, to monitor data and write values to devices.

The Modbus protocol is a communication method developed by Modicon in the 80s for sending and receiving information between electronic devices. Protocol is based on master-slave architecture and can be used with different interfaces – RS-232, RS-485 and TCP/IP also. Master(client) is called the device requesting information and slave(server) is the device sending information. Connect21 works as master and slave with unlimited socket connections and different data types.

Modbus is the most available open protocol used by many manufacturers is industry. Modbus is typically used for sending information such as temperature, pressure, flow to data collecting system or data acquisition system (SCADA).

The master connects to slaves using a unique ID. The protocol supports up to 247 addresses.

Slave devices have a Modbus address register map (registers) where all data is stored. Each register is 16 bits of data. Register map is divided to 4 main groups(functions): Coils, digital inputs, analogue inputs, holding registers. Coils and digital Inputs are always binaries, others – may vary with devices

Access to registers is implemented by different functions, depending on requested register. You can read coil registers by function 1(Read coils) and write by function 5(Write coil) or 15(write multiple coils). In a certain way - Read holding registers (03) and Write holding register (06) or Write multiple holding registers (16) It is not allowed to write to discrete and analogue inputs, but it is available by functions 2 and 4 respectively.

Connect21 is freeware with unlimited usage time, with no ads, no banners and other nonsense.

Connect21 is usefull for testing Modbus connection with such devices as PLCs, frequency converters, sensors and many other Modbus devices with writing data to SQL database. It can simulate sensor work for testing PLC program as well.

Special program to imitate analogue or digital output. There are 3 functions available - flip-flop, saw and sine, which can be assigned to any Modbus server address for testing. Saw and sine functions can be adjusted to imitate real sensor work.

You can use datalogging to store information to the database. A database stores information in tabular form, with rows and columns representing different data attributes.

SQL(Structured Query Language) is a programming language for storing and processing information in a database.

Currently Microsoft SQL server only is supported.

Enter value 'Now' in value column for writing current datetime to the datebase. Use quotation marks.

SQL server has 2 authentication types. SQL server authentication and Windows authentication. Use Windows authentication to use Windows account for connecting SQL server. This means that the user identity is confirmed by Windows. UserID and password not needed for Windows authentication. Use UserID and password for SQL authentication. Find out how to enable SQL authentication for server in SQL documentation.

Each value has its own unique name. It can be an address on the server or client, or a simulated value.

To assign a tag to a value, it is necessary to drag and drop it from the "tag name" field to the "value" field.