Link Mode

Keywords: Link Mode, Connection, Start Up, link, mode,


Summary:

Information on how a sensor connects to the network. What is Link Mode?



When the batteries are inserted in a sensor, the sensor tries all of the available channels to find a gateway. This is called “Link Mode," where the sensor starts on the first channel and sends a message, “I’m number 12345, can I talk to you?" If it doesn’t hear anything back it assumes there is not a gateway on that channel, and tries the second channel. After it has tried all of the channels and determines there is no available gateway, it stops sending messages for two hours.

Each scan-cycle takes about 30 seconds, but uses over a day’s worth of battery power. In other words, if it just continued to scan continually when the gateway wasn’t powered on, it would burn out very quickly. After two hours it starts the process over again beginning with the first channel. Similarly, if for instance the sensor was talking to the gateway on channel 15, but has multiple failed transmissions (2 heartbeats each with a report, plus two retries, and six missed communications in a row) assumes the gateway it was communicating with is no-longer available and enters the same “Link Mode”.

This is important because if the battery is put in the sensor before the gateway is active and ready to listen for the sensor, the sensor will miss the gateway and not scan again for another two hours. In order to get the sensor to scan again more quickly, you must remove the batteries for at least 60 seconds. This alows the processor to completely un-power. Then put the batteries back in so it will start scanning right away. If the batteries are out only for a few seconds, the processor is still running off board capacitance and doesn’t “re-boot” when the batteries are put back in.

For the best start-up experience, make sure gateways are active and powered-on before you put the batteries in your sensors, so they can boot up and find the gateway on the first scan. If batteries are in the sensors before the gateway has gone active, then it will take two hours to join the network and start to report their readings.



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