Bluetooth Device Modes
Although you can incorporate Bluetooth radios in ordinary PCs, they were originally designed to be used for low-power devices. Because of this, it isn't necessary for the Bluetooth device to be in an active stateconsuming powerall the time. Before a piconet is formed, a device is in standby mode, in which a device will listen for messages every 1.28 seconds. To initiate a connection with another device, an inquiry message is sent, which is used to find other Bluetooth devices within the transmission range. If the address of the device to which a connection is desired is already known, a page message is used instead to begin the communication session.
In addition to being involved in active communications (the active mode), a device can be put into three other modes:
Hold A master unit can put a slave unit into hold mode, or the slave unit can request that it be placed into this mode. This is a power-saving mode in which the unit no longer actively exchanges data with other devices. Sniff In this mode, the device does not actively participate in communications with other devices. Instead, the device "wakes up" and listens for messages frequently. How often this occurs depends on the particular application for which the device is used, and the frequency is programmed into the device by the manufacturer. A master device can request that a slave device be put into sniff mode, but cannot force it to. Park In this low-power mode, the device is still considered to be part of a piconet, but no longer has an Active Mode Address (AM_ADDR) associated with it. The device listens for broadcast messages and resynchronizes its clock with the master, but does not actively communicate. Before a device enters Park mode, the master will assign a Park Mode Address (PM_ADDR) to the device, easing the process of re-establishing active communications in the future.
These different modes are mainly designed to allow for different levels of low-power consumption for a Bluetooth-enabled device.
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