CC1101
SWRS061H Page 55 of 98
FS Calibration Time
f
xosc
= 26 MHz
FS Calibration Time
f
xosc
= 27 MHz
Table 35: Frequency Synthesizer Calibration Times (26/27 MHz crystal)
19.7 RX Termination Timer
CC1101
has optional functions for automatic
termination of RX after a programmable time.
The main use for this functionality is Wake on
Radio, but it may also be useful for other
applications. The termination timer starts when
in RX state. The timeout is programmable with
the MCSM2.RX_TIME setting. When the timer
expires, the radio controller will check the
condition for staying in RX; if the condition is
not met, RX will terminate.
The programmable conditions are:
MCSM2.RX_TIME_QUAL=0: Continue
receive if sync word has been found
MCSM2.RX_TIME_QUAL=1: Continue
receive if sync word has been found, or if
the preamble quality is above threshold
(PQT)
If the system expects the transmission to have
started when enabling the receiver, the
MCSM2.RX_TIME_RSSI function can be used.
The radio controller will then terminate RX if
the first valid carrier sense sample indicates
no carrier (RSSI below threshold). See Section
17.4 for details on Carrier Sense.
For ASK/OOK modulation, lack of carrier
sense is only considered valid after eight
symbol periods. Thus, the
MCSM2.RX_TIME_RSSI function can be used
in ASK/OOK mode when the distance between
“1” symbols is eight or less.
If RX terminates due to no carrier sense when
the MCSM2.RX_TIME_RSSI function is used,
or if no sync word was found when using the
MCSM2.RX_TIME timeout function, the chip
will always go back to IDLE if WOR is disabled
and back to SLEEP if WOR is enabled.
Otherwise, the MCSM1.RXOFF_MODE setting
determines the state to go to when RX ends.
This means that the chip will not automatically
go back to SLEEP once a sync word has been
received. It is therefore recommended to
always wake up the microcontroller on sync
word detection when using WOR mode. This
can be done by selecting output signal 6 (see
Table 41 on page 62) on one of the
programmable GDO output pins, and
programming the microcontroller to wake up
on an edge-triggered interrupt from this GDO
pin.
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