Linx HumPRC Series Data Manual page 20

Using the Low Power Features
The module supports a sleep state to save current in battery-powered
applications. During the sleep state, no module activity occurs and no
packets can be received but current consumption is less than 1µA typical.
There are two ways of putting the module to sleep. First, pulling the Power
Down (POWER_DOWN) line low puts the module to sleep. Taking the line
high wakes the module. Second, all of the following should be true:
1. There is no transmission in progress
2. All status lines are low and either
• IDLE = 1 (default) and all status lines are configured as inputs, or
• IDLE = 2 (allows sleeping when incoming control message may be
missed)
3. The internal KeepAlive timer has expired.
The internal KeepAlive timer is set by the following events:
1. On wakeup from a transition on the CMD_DATA_IN line, KeepAlive is
set to 2s. This allows time for an external unit to change IDLE to 0 to
keep the unit awake.
2. On each transmission, KeepAlive is set to 760ms if the remaining
KeepAlive time is less. [max(760ms, KeepAlive)]
3. On reception of a REMOTE_CONFIRM packet, KeepAlive is
set to received ALIVE value multiplied by 0.1s if the remaining
KeepAlive time is less. The KeepAlive can be extended indefinitely
by periodic reception of REMOTE_CONFIRM messages.
max(REMOTE_CONFIRM.keepAlive * 100ms, KeepAlive)
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During sleep mode, the output lines are in the states in Figure 27.
HumPRC Series Transceiver Output Line Sleep States
TM
Output Line
S0 - S7 output
LNA_EN
PA_EN
CMD_DATA_OUT
MODE_IND
ACK_OUT
Figure 27: HumPRC TM Series Output Line Sleep States
When the POWER_DOWN line is high, the module awakens when a status
line input goes high, the PB line goes high or there is a change on the
CMD_DATA_IN lines. If a negative-going pulse is needed to generate a
rising edge, the pulse width should be greater than 1µs.
If the volatile registers have been corrupted during sleep, a software reset
is performed. This restarts the module as if power were cycled. This can be
caused by power surges or brownout among other things.
Pulsing RESET low causes the module to restart rather than continue from
sleep.
IDLE = 1 is used when the module is an IU only. This puts it to sleep when
all status line inputs are low.
IDLE = 2 is used when the module is primarily an IU, but can accept
activation commands from remote units. In this case, the module stays
asleep until a status line input goes high. While awake, the module can
receive activation commands and will remain awake while commands are
received. As soon as all status line inputs and outputs go low, the module
returns to sleep.
Sleep State
Low
Low
Low
Low
Low
Low
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