Z-Wave Primer

This document covers some important aspects of the Z-Wave application-level standard that you may come in contact with when developing Device Handlers for Z-Wave devices. If you are already familiar with Z-Wave development, you can learn how SmartThings integrates with it in Building Z-Wave Device Handlers. You can also consult the Z-Wave public specification for more information about the Z-Wave protocol.


Command classes

Z-Wave device messages are all called “commands”, even if they are just info reports or other kinds of communications. They are organized into command classes which group related functionality together. Some devices list which command classes they support in their manuals.

There is a list of the command classes that SmartThings supports here: Z-Wave Command Reference. Notice some of them have multiple versions. The Z-Wave standard occasionally adds a new version of a command class that may add new commands or add more data fields to existing commands. New versions are backwards-compatible and generally our command parsing system can handle different versions interchangeably, but you may need to specify a specific version in some cases.

Some commonly seen command classes:

  • A generalized get/set/report command class that all devices support. It is usually mapped to another more specific command class, like Switch Binary for switches or Sensor Binary for sensors.
  • Control of on/off switches.
  • Control of dimmer switches.
  • Sensors with two states, such as motion detectors and open/closed sensors.
  • Sensors that report a numeric value, like temperature or illuminance.
  • Outlets and meters that measure energy use.
  • The Alarm command class was renamed to Notification in version 3.
    Used by sensors and other devices to report events.
  • See Configuration section below.
  • Battery level reporting for battery powered devices.
  • See Listening and Sleepy Devices section below.
  • See Association section below.
  • All devices report their Z-Wave framework and firmware version on request.
  • All devices report their manufacturer and model (via numeric code).
  • Commands to and from security-sensitive devices can be sent encrypted by wrapping them in SecurityMessageEncapsulation commands.
  • The Multi Instance command class was renamed to Multi Channel in version 3. It is used by devices to distinguish between multiple control or reporting end points.

Listening and sleepy devices

Z-Wave devices that are plugged in to power are called listening devices because they keep their receiver on all the time. Listening devices act as repeaters and therefore extend the Z-Wave mesh network.

Battery powered Z-Wave devices such as sensors or remote controllers are sleepy – they turn off their receivers to save energy, so you can’t send them commands at any time. Instead, they wake up at a regular interval and send a WakeUpNotification to alert other devices that they will be listening for incoming commands for the next few seconds. The WakeUpIntervalSet command is used to configure both how often the device will wake up and which controller it will send its WakeUpNotification to. When the controller gets the WakeUpNotification and has no commands to send to the device, it can send WakeUpNoMoreInformation to tell the device that it can go back to sleep.

Some battery powered devices like door locks and thermostats have to be able to receive commands at any time. These are known as beamable devices, because they wake up for only a tiny slice of time each second or quarter-second and listen for a “beam”. Thus, the sending device must “beam” the receiving device for a full second to wake it up fully before sending a command. This makes communication with these devices take a significantly longer time than with a normal listening device.


Configuration

A Z-Wave device can use the Configuration command class to allow the user to change its settings. Configuration parameters and their interpretation vary between device models, and are usually detailed in the device’s manual or technical documentation.

The command class includes commands to read and set configuration parameter values. One thing to be careful of is that the ConfigurationSet command encodes the setting value in a 1, 2, or 4 byte format, and many devices will only properly interpret the value if it is sent in the same byte format. When sending a ConfigurationSet, make sure to set the ‘size’ argument to the same value as it has in an incoming ConfigurationReport from the device for the parameter number in question.


Association

The Association command class is used to tell a Z-Wave device that it should send updates to another device. It provides the ability to add associated devices to different numbered groups that can have different meanings. This functionality is used in a few different ways, often detailed in the device’s manual or technical documentation:

  • Some sensors will send reports of the events they detect only to devices that have been added to a specific association group.
  • Many sensors will send BasicSet commands to associated devices, for example to turn a light on when a door opens and off when it closes.
  • Some devices have multiple groups for different uses, like group 1 gets sent BasicSet commands, group 2 gets sent SensorBinaryReport events, and group 3 gets sent BatteryReport updates.
  • Most door locks will send status updates to associated devices when they are locked or unlocked manually.

The SmartThings Hub automatically adds itself to association group 1 when a device that supports association joins the network. If this is inappropriate for your Device Handler, your Device Handler can use AssociationRemove to undo it. To associate to a group higher than 1, the Device Handler can send AssociationSet. The Hub’s node ID is provided to Device Handler code in the variable zwaveHubNodeId.