User Manual

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CCT24
2.15 Sleep Modes
To save power in applications where a remote transmits infrequently, the CCT24 supports hardware and
firmware sleep modes. Hardware sleep mode is entered by switching SLEEP/DTR Pin 11 on the CCT24
from logic low to high. While in hardware sleep mode, the CCT24 consumes less than 50 µA at room
temperature. This mode allows a CCT24 to be powered off while its host device remains powered. After
leaving hardware sleep mode, the radio must re-synchronize with the base and re-register. Note that
sleep mode is not available on tree-routing routers.
In addition to the sleep mode controlled by Pin 11, in CSMA mode the CCT24 remotes support an addi-
tional sleep mode to support battery-powered applications. When this mode is enabled, the CCT24 is in a
low-power state and only wakes up in response to the I/O report triggers. The following list explains the
rules that sleeping remotes follow:
 The CCT24 will wake up when any of the enabled I/O report trigger conditions fire. When any of
the ADC triggers are enabled, the radio will also wake up every ADC_SampleIntvl long enough to
sample the ADCs, and then go back to sleep.
 When a sleeping radio wakes up, it must acquire and synchronize to its base before it can send
or receive any data. To prevent excessive battery use, if the remote is unable to acquire before
the WakeLinkTimeout elapses (because it is no longer in range, for example), it will cancel any
pending event trigger(s) and go back to sleep.
 If a remote is linking for the first time or if its last attempt to acquire and synchronize was unsuc-
cessful, it will scan and record the entire broadcast system parameter list before it goes back to
sleep. Otherwise, in order to conserve battery life, a sleeping remote will update any values that it
may hear while it is awake, but is not required to listen to the entire list.
 If a remote is linking for the first time or if its last attempt to acquire and synchronize was unsuc-
cessful, it will send a registration request to the base, allowing it to announce its presence to the
host. Otherwise, in order to conserve battery life, a sleeping remote will not register each time it
reacquires link with its base on successive wakeups.
 After a remote has received an acknowledgement for its I/O report, a WakeResponseTime timer
is started before the remote goes back to sleep. This allows the base host time to send a mes-
sage to the remote. Note that the only notification that the base host application has that a remote
is awake is its report packet. In order to send it data, the base host must ensure that the message
is transmitted and received before the remote's WakeResponseTime window elapses. If this func-
tion is not needed, the WakeResponseTime can be set to zero to disable it.
The lease renewal mechanism is not supported for sleeping remotes. In order to successfully use sleep-
ing remotes, the user must ensure that the system is configured for CSMA mode and that leases are
disabled. If these settings are not used, there is no guarantee that the remotes will be able to communi-
cate reliably. Because leases are not supported, there is no built-in mechanism for the base to detect or
announce to its host if a remote leaves the network.
To summarize, while a remote is awake, the following list of condition checks are used to determine if and
when it is allowed to go back to sleep: