MRF39RA Datasheet, PDF (22/72 Pages) Microchip Technology – Low-Power, Integrated UHF Receiver

MRF39RA
3.2.2 Rx Start Procedure
As described in the previous sections, the RxReady
interrupt warns the uC that the receiver is ready.
• In Continuous mode with bit synchronizer, the
receiver starts locking its bit synchronizer on a
minimum or 12 bits of received preamble before
the reception of correct data or sync word (if
enabled) can occur. See Section 2.4.14 “Bit
Synchronizer” for details.
• In Continuous mode without bit synchronizer,
valid data is available on DIO2/DATA right after
the RxReady interrupt.
• In Packet mode, the receiver starts locking its bit
synchronizer on a minimum or 12 bits of received
preamble before the reception of correct data or
sync word (if enabled) can occur. See
Section 2.4.14 “Bit Synchronizer” for details.
3.2.3 Optimized Frequency Hopping
Sequences
In a frequency hopping-like application, it is required to
turn off the receiver when hopping from one channel to
another, to optimize the hopping sequence:
Receiver hop from Ch A to Ch B:
1. MRF39RA is in Rx mode in Ch A
2. Change the carrier frequency in the RegFrf
registers
3. Program the MRF39RA in FS mode
4. Turn the receiver back to Rx mode
5. Respect the Rx start procedure, described in
Section 3.2.2 “Rx Start Procedure”.
3.3 Listen Mode
To set the circuit to Listen mode, ListenOn in
RegOpMode must be set to ‘1’ while in Standby mode.
In this mode, MRF39RA spends most of the time in
Idle mode, during which only the RC oscillator runs.
Periodically the receiver wakes 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 is not detected after a
predefined 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 MRF39RA, it is
locally handled by the Listen mode block without using
uC resources or energy.
The simplified timing diagram of this procedure is
illustrated in Figure 3-4.
Note:
The sequence assumes that the
sequencer
is
turned
on
(SequencerOff = 0 in RegOpMode).
FIGURE 3-4:
LISTEN MODE SEQUENCE (NO WANTED SIGNAL IS RECEIVED)
t_ListenIdle
Rx
Idle
Rx
time
t_ListenRx
t_ListenRx
DS40001778B-page 22
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