Rev 4.9
SignalFire Telemetry
6
Operation
The Gateway-In-A-Stick supports all remote SignalFire nodes making all remote sensor data
available in Modbus format.
The register data from remote sensor nodes is available by requesting the remote node’s Modbus
ID and register address from that node’s register map. The gateway will respond with the most recent copy of
the data from the remote node. The gateway will automatically time-out data from a remote node it stops
receiving data for.
If the remote node is a Modbus-Stick interface node additional features are supported.
Remote Modbus Sticks and Sentinel-Modbus (non-sleeping radio only) Nodes
Remote nodes that have been pre-configured forward their set of registers to the Modbus gateway on a pre-
defined schedule (1 minute to 5 minutes is typical). The register data is then buffered in the gateway and is
available to be read by the RTU at any time.
If a Modbus request is received by the gateway for a Modbus ID and address for which buffered data does not
exist, but the Modbus ID is known, the Modbus request will be forwarded to the remote Modbus node over the
SignalFire network. The response is returned to the RTU.
If a request for multiple registers is issued by the RTU, and if the gateway does not have all registered data
buffered, an exception will be returned. The system will not combine buffered and transparent data within a
single Modbus response.
Remote Modbus Stick Node Re-Scan
It is possible to cause a remote Modbus Stick to re-scan for attached Modbus devices by writing to one of the
gateway’s configuration registers. This is useful to discover a Modbus device that is added to an existing
Modbus node. The scan may be initiated by one of the two methods. First, if the radio address of the Modbus
Stick is known, writing this address to gateway register 3000 will result in a scan. Second, if the Modbus ID of
one of the already registered devices attached to a Modbus Stick is known, a scan will be started by writing the
ID to gateway register 3002.
