Connection problems

7 min readTroubleshooting

A connection cannot be established or drops in Live: finding out which layer a message comes from, common network-level messages, timings, and the right driver topic according to the beginning of the message.

First find the layer

The cause of a connection problem lies in one of four layers: the connection definition, the network, the protocol session of the device, or the individual tag addresses. Live tells you which layer it is stuck at with the red message in the system menu. The detailed message table of each driver is in its own topic; this topic takes you from the message to the right topic and explains the network messages shared by all drivers.

Connection definition
If the state in the System menu › Connections section is no driver, the driver ID is not recognized; the connection is never attempted. A connection with Enabled turned off appears as inactive (disabled) (Connections table).
Network
If the connection shows no connection and the message says did not respond or no network access, a TCP connection to the device cannot be established. See the table below.
Protocol session
If the traffic gets through the network but the message mentions S7, OPC UA, MQTT, MC, FINS or EtherNet/IP, the problem is in the settings of the device (PUT/GET permission, security policy, slot number, data code…). Look for the message in the relevant driver topic.
Tag address
If the connection shows connected but some values do not arrive, it is an address problem. The tag-specific error text is not displayed in Live in this version; see the Tag errors section in Connection diagnostics.

Messages seen at the network level

The following messages have the same form in the S7, Modbus TCP, Allen-Bradley, Mitsubishi MC and Omron FINS drivers. They appear in red text below the connection in the system menu.

Message	Meaning	What to do
`Bağlantının IP adresi boş.`	The address field is empty in the connection row.	In the Connections table, fill in the address and upload the project to Live again.
`Cihaz N ms içinde yanıt vermedi (IP:port). IP adresini ve ağ bağlantısını kontrol edin.`	The TCP connection to the port could not be established. N is the smaller of the Timeout and 3000 ms.	Check the IP address, the cable, the switch, the network of the Live computer and the firewall.
`Cihaza ağ erişimi yok (IP:port): …`	The connection attempt returned an error from Windows (without waiting for the timeout). The rest of the message is the network error given by Windows.	Read on: if the target cannot be reached, the IP address and subnet; if the connection was refused, the port number or the device not having enabled that protocol.
`Cihaz yanıt vermedi (zaman aşımı).` · `PLC yanıt vermedi (zaman aşımı).`	The connection had been established; the request went unanswered.	If the device is busy or behind a gateway, increase the Timeout value.
`Cihaz ile bağlantı koptu (ağ, kablo ya da cihaz kapalı olabilir).` · `PLC ile bağlantı koptu (…)`	The other side closed the connection or the network went down while the connection was running.	Check the cable, power and network devices; the driver reconnects automatically.
`Cihaz bağlantısı kapalı.` · `OPC bağlantısı kapalı.`	A request was issued while the connection was closed; reconnection is in progress.	It is usually short-lived. If it is permanent, one of the messages above should also appear.

The other drivers have their own equivalents:

OPC UA: OPC UA sunucusu bağlantı isteğine yanıt vermedi (zaman aşımı). and OPC UA sunucusu ile bağlantı koptu (ağ, kablo ya da sunucu kapalı olabilir) (BadXxx). The Bad… in parentheses is the OPC UA status code; look it up in the server manufacturer's documentation.
MQTT: MQTT sunucusu N ms içinde yanıt vermedi (…), MQTT sunucusuna ağ erişimi yok (…) and MQTT sunucusuyla bağlantı koptu: …. If nothing arrives from the server for 1.5 times the Keep-alive interval, MQTT sunucusundan N sn'dir hiçbir şey gelmedi; bağlantı koptu sayıldı (canlı tutma süresi N sn). is displayed.
OPC DA: OPC sunucusuyla haberleşme koptu (…) (for DCOM / RPC details, see OPC DA driver).

Test the network from the Live PC

The Online›Test connections… command in Studio tests the network from the computer on which Studio runs. If Live is on another computer, the result may differ; perform the network test on the Live computer.

Reach the address
Try ping <IP> at the command prompt. Some devices do not respond to ping; the lack of a response is not proof on its own.
Test the port
In PowerShell, run Test-NetConnection <IP> -Port <port>; you should see TcpTestSucceeded : True.
Make sure that you use the correct port
Ports suggested by Studio:

Driver	Default port
S7-300 / 1200 / 1500	102
Modbus TCP	502
OPC UA	4840
Allen-Bradley EtherNet/IP	44818
Mitsubishi MC Protocol	5007 (the port of the connection you open in the PLC applies)
Omron FINS	9600
MQTT	1883 (usually 8883 for TLS)

Timings

Topic	Behavior
Timeout	Timeout (ms) in the connection row; default 2000, limit 100 – 60000. When connecting, at most 3 s is waited.
Reconnection	A connection that cannot be established or that drops is retried after 1 s, 2 s and 5 s, and then every 10 s. If a connection drops after having stayed up for 10 s or longer, the wait starts again from 1 s.
At startup	Until the first attempt ends, the connection shows as no connection and the message line is empty; the connecting state is not shown.
Unreadable tag	The tag is removed from the read set while the other tags continue to be read; it is retried every 30 s. Once the address is corrected or the data block is loaded to the PLC later, reading recovers by itself within this interval.
Write	Writing is rejected while the connection is down: `Bağlantı kopuk: <bağlantı adı>`. A write waiting in the queue is rejected with `Bağlantı koptu: <bağlantı adı>` if the connection drops. The messages seen by the operator are in the Operator guide.

The right topic for the message

If the message mentions	What to check
S7 connection could not be opened, PUT/GET, Optimized block access, Data block does not exist in the PLC	Siemens S7
Security option, anonymous logon, certificate, endpoint path, session limit, NodeId	OPC UA and Connection security
Modbus exception 01 – 0B, Invalid Modbus response	Modbus TCP
EtherNet/IP, CIP status, slot, Micro800, External Access	Allen-Bradley
MC end code, data code (Binary / ASCII), Enable online change	Mitsubishi MC
FINS, FINS/TCP error code, node number	Omron FINS
OPC server, ProgID, DCOM, RPC, OPC Core Components	OPC DA
MQTT server, subscription, client ID, JSON path	MQTT
Messages that ask for a user name / password	Connection security and Enter password in the system menu

Frequently dropping connection

A state is written to the event log only if it lasts at least 2 s; if more than 5 changes occur within 60 s, a single Connection unstable entry is logged. If you see this entry in the event view, first rule out the cable, the network switch or the device's network card.
Connection drops are not written to the program's logs file; only unexpected driver errors are written (Log files).
To bind the connection status to a warning lamp or an alarm, use the <Bağlantı adı>_Baglanti status tag (Connection diagnostics).

Before requesting support

Collect the following: the driver and settings of the connection (excluding passwords), the message text in the system menu (screenshot), the result of Test connections and the output of Test-NetConnection on the Live computer.