Connect a Modbus TCP device

Modbus TCP devices are polled over the network by a gateway on the same LAN.

Protocol: modbus-tcp

Connection fields:

Set the Modbus Device ID. One IP address often fronts several Modbus units — a serial-to-Ethernet converter or a multi-meter panel answers for each of them on the same socket, distinguished only by unit ID. Leave it at 1 only if the device genuinely is unit 1; otherwise reads either time out or, worse, return another unit's registers.

Steps

1. Give the device a static IP (or DHCP reservation) on the gateway's network.
2. Add a device with protocol modbus-tcp and enter the fields above.
3. Map registers to tags.

If reads time out, confirm the IP/port are reachable from the gateway and the unit ID is correct.

Publish interval vs read interval. These are two different things:

• Publish interval is how often readings reach Synacl. It counts against your plan's rate limit. Devices on a gateway publish at most once per 10 seconds, so lower values change nothing.
• Read interval is how often the gateway actually queries the device. Threshold alerts and macros running on the gateway react at this rate, so leave it fast even when you publish slowly — you can poll a pump every 10 seconds for a trip condition while only reporting to the cloud once a minute.

Directly-polled Modbus TCP devices (no gateway) have no separate read interval — the backend poller reads and stores in one step, and it skips any device set below 1000 ms entirely.

Auto-disable after repeated failures: for a directly-polled Modbus-TCP device, if a poll fails 10 times in a row Synacl stops querying it and marks it Polling disabled (a device/poll-disabled event is raised). Fix the cause, then click Re-enable polling on the device page — querying resumes within about a minute. See My device shows offline.