CC112X/CC1175
SWRU295C
Page 62 of 108
8.7.1
RX Sniff Mode Usage
RX Sniff Mode is extremely useful in cases where you do not know when the transmitter is going to
send a packet. Figure 29 shows ordinary RX mode, where the radio must stay continuously in RX to
make sure that it will receive the transmitted packet.
Time
TX
Payload
Sync
RX
4 bits
preamble
Figure 29: Ordinary RX Mode
By increasing the preamble of the transmitted packet, the receiver can implement RX Sniff Mode and
wake up at an interval that ensures that at least 4 bits of preamble is received. RX termination based
on CS greatly reduces the time in RX and forces the radio back in SLEEP if there is no signal on the
air.
Time
TX
Payload
Sync
R
X
Preamble
(4 bytes)
RX
R
X
R
X
Figure 30: RX Sniff Mode
The wake-up interval (t
Event0
) can be increased further by letting the receiver look for an 11 bits sync
word (16 bits are sent on the air). This way, the 5 MSBs can be used for AGC settling and no
preamble is needed (see Figure 31).
Time
TX
Payload
Sync
R
X
Preamble
(4 bytes)
RX
R
X
R
X
Figure 31: RX Sniff Mode (no preamble)