SX1231
ADVANCED COMMUNICATIONS & SENSING
4.3. Listen mode
DATASHEET
The circuit can be set to Listen mode, by setting ListenOn in RegOpMode to 1. In this mode, SX1231 spends most of the
time in Idle mode, during which only the RC oscillator runs. Periodically the receiver is woken up and listens for an RF
signal. If a wanted signal is detected, the receiver is kept on and the data is demodulated.
Otherwise, if a wanted signal hasn't been detected after a pre-defined period of time, the receiver is disabled until the next
time period.
This periodical Rx wake-up requirement is very common in low power applications. On SX1231 it is handled locally by the
Listen mode block without using uC resources or energy.
The simplified timing diagram of this procedure is illustrated in Figure 18.
tListenIdle
Rx
Idle
Rx
time
tListenRx
tListenRx
Figure 18. Listen Mode Sequence (no wanted signal is received)
The duration of the idle phase is given by t
. The time during which the receiver is on and waits for a signal is given
ListenIdle
by t
. t
includes the wake-up time of the receiver, described in section 4.2.3. This duration can be
ListenRx ListenRx
programmed in the configuration registers via the serial interface.
Both time periods t and t (denoted t in the following text) are fixed by two parameters from the
ListenRx
ListenIdle
ListenX
configuration register and are calculated as follows:
tListenX = ListenCoefX ⋅ ListenResol
where ListenResol gives the Rx/Idle common resolution and is programmable on three values (1, 2 and 3), whereas
ListenCoefX is an integer between 1 and 255. All parameters are located in RegListen registers.
The timing ranges are tabulated in Table 15 below.
Table 15 Range of Durations in Listen Mode
ListenResol
Min duration
Max duration
( ListenCoef = 1 )
( ListenCoef = 255 )
0101
1010
1111
64 us
4.1 ms
0.26 s
16 ms
1.04 s
67 s
Rev 2 - Nov 2009
Page 37
www.semtech.com
SEMTECH [ SEMTECH CORPORATION ]
