Connections

For drivers that need a network address, two connections cannot use the same address (except OPC DA and MQTT), so the same PLC cannot be reached with S7 and OPC UA at the same time. With the serial drivers the same COM port is used by several connections: one connection per device on the RS-485 line. For every connection an internal Bool tag, named after the connection like PLC_Proses_Baglanti, is added automatically. Live writes its value (1 = connected); it can be used in animations, alarms and scripts.

The data type list of a tag narrows to the types the driver of its connection supports, and the address is validated against the rules of the driver. Modbus RTU and ASCII work over a serial port, OPC DA over COM / DCOM, and the other drivers over Ethernet. There is no serial protocol other than Modbus; for other serial devices use an Ethernet gateway or an OPC server.

These rules apply to all PLC drivers.

• Each connection runs in its own thread; a device that does not respond does not delay the other connections.
• A read cycle of at least 100 ms is applied for PLC and simulator tags. Only changed values are passed on, at most every 100 ms per connection.
• Writes are made between reads and the written tag is read back. A write is rejected while the connection is down.
• If the connection cannot be made or drops, the driver retries after 1 s, 2 s and 5 s, then every 10 s.
• A tag that cannot be read is removed from the read set and retried every 30 s; the other tags are not affected.

Studio never connects to a device. Online › Test connections… shows for each connection whether a TCP connection can be opened (it waits at most 2 s); simulator and serial connections are skipped. No protocol test is made: the S7 session, the PUT/GET permission, the OPC UA security selection, the user name and the password are tried only in Live. The Diagnostics tab of the Inspector lists the target and the number of bound tags of each connection.

The states appear in the Connections section of the Live system menu and in the PLC connection status control placed on a screen. The Event view shows the connection established, lost, could not be established and unstable entries.

Even when the connection is up, a single tag may be unreadable, for example with a wrong address or a data block that does not exist. Only that tag gets bad quality and the connection stays Connected. An object bound to a bad-quality tag is drawn faded gray. The message the driver produces for a tag error is not shown in Live; to find the cause, verify the address in Studio and check the error table on the driver page.

For OPC UA, MQTT and OPC DA connections the user name stays in the project and the password does not. The password is not written to the project file; sharing, backing up or uploading the project to Live does not carry it. You enter the password in Live:

• The Settings authorization is required to enter a password.
• In the Connections section of the system menu, click the Enter password button next to the connection that asks for one.
• Type the password and press Save. Communication restarts and the connections drop and reconnect briefly.

If an MQTT client certificate is read from a PFX file, the PFX password is entered in the same window. The password you enter is stored unencrypted in the baglanti_sifreleri.json file in the data folder of the project on the Live computer. Open the folder only to the account that runs Live, using Windows permissions.

• Automatic switchover to a backup PLC exists only in the S7 drivers; with the other drivers a connection has a single address.
• Enabled is set only in the design. There is no button or function to switch a connection on and off while Live is running.
• After changing a connection setting, save the project and upload it to Live; Live establishes the connections when the project is opened.
• The Operating mode in Device configuration runs Live as a single station or as a redundant server pair. On a single station, Live warns if it is opened on a computer other than the one named in the project.