I have to do a network of devices based on MCU. This network in a RS485 and the device is battery powered.

For save the battery I put the MCU into sleep mode and I want to wake the MCU up, when there's a RS485 communication to process the incoming packets and return in sleep mode.

I read the feature of many RS485 transceivers and I saw that they use a quiestent current of 1 mA.

I saw also that is possible put in sleep mode some kind of transceiver.

Is possible to put the transceiver in sleep mode and wake it up with the MCU when the RS485 line become busy?

Which kind of IC I have to use?

  • \$\begingroup\$ On this site you've asked the same question but also mentioned you MCU is PIC. Is this still the case? Because "what kid of wake up events does my MCU handle?" must be the first question when designing this kind of device, not about the transceiver chip. \$\endgroup\$ – Maple Jan 19 '20 at 7:10
  • \$\begingroup\$ And the second most important question should be "what kind of wiring will my network use?". If you are responsible for the wiring, can you run a 4-conductor cable instead of required 3-conductors? Without answering these two questions your question about transceiver chip is pointless, and should be closed IMHO \$\endgroup\$ – Maple Jan 19 '20 at 7:23
  • \$\begingroup\$ LOL... just realized that this question has been abandoned long time ago \$\endgroup\$ – Maple Jan 19 '20 at 8:56

The DS36C279 is a RS485 transceiver with sleep mode, with a sleep mode current of 10uA. When you disabled both transmit and receive it enters sleep mode. The difficulty in using this part is that it cannot automatically wake an MCU from sleep, because when itself is in sleep it cannot receive data from the RS485 network.

You will need to design your system rather like a low power wireless system, where all nodes wake up at the same time to check if there is a transmission in progress that they need to receive. This synchronisation is often done at 1 to 10 second intervals, but you can chose the interval depending on the response time that you need. The real art of designing a good wireless system is maintaining precise synchronisation over a long period of time. But that's a different question.

  • \$\begingroup\$ Whether or not MCU can receive data while asleep is irrelevant for the task. First, some MCUs have interfaces that can be left running in sleep mode and even process incoming packages for "wake up on pattern match" function. But even without that, wake up time time even on fastest MCUs will probably mean lost data of the first incoming package. Meaning that either special wake-up signal should be sent in advance or the same package should be re-transmitted. In both cases there are many HW solutions available without complexity of time synchronization \$\endgroup\$ – Maple Jan 19 '20 at 7:39

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