RFM12B_15 Datasheet, PDF (25/41 Pages) List of Unclassifed Manufacturers – Universal ISM Band FSK Transceiver

RFM12B
14. Wake-Up Timer Command
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 1 r4 r3 r2 r1 r0 m7 m6 m5 m4 m3 m2 m1 m0
POR
E196h
The wake-up time period can be calculated by (m7 to m0) and (r4 to r0):
T wake-up = 1.03 · M · 2^R + 0.5 [ms]
Note:
• For continual operation, the ew bit should be cleared and set at the end of every cycle.
• For future compatibility, use R in a range of 0 and 29.
15. Low Duty-Cycle Command
Bit 15 14 13 12 11 10 9
1100100
876543210
0 d6 d5 d4 d3 d2 d1 d0 en
POR
C80Eh
With this command, autonomous low duty-cycle operation can be set in order to decrease the average power consumption in receive
mode.
Bits 7-1 (d6-d0): The duty-cycle can be calculated by using (d6 to d0) and M. (M is parameter in a Wake-Up Timer Command, see
above). The time cycle is determined by the Wake-Up Timer Command.
duty-cycle= (D · 2 +1) / M · 100%
Bit 0 (en): Enables the low duty-cycle Mode. Wake-up timer interrupt is not generated in this mode.
Note: In this operation mode, bit er must be cleared and bit ew must be set in the Power Management Command.
In low duty-cycle mode the receiver periodically wakes up for a short period of time and checks if there is a valid FSK transmission in
progress. FSK transmission is detected in the frequency range determined by Frequency Setting Command plus and minus the
baseband filter bandwidth determined by the Receiver Control Command. This on-time is automatically extended while DQD
indicates good received signal condition.
When calculating the on-time take into account:
- the crystal oscillator, the synthesizer and the PLL needs time to start, see the AC Characteristics (Turn-on/Turnaround
timings)
- depending on the DQD parameter, the chip needs to receive a few valid data bits before the DQD signal indicates good
signal condition (Data Filter Command)
Choosing too short on-time can prevent the crystal oscillator from starting or the DQD signal will not go high even when the received
signal has good quality.
There is an application proposal. The RFM12B is configured to work in FIFO mode. The chip periodically wakes up and switches to
receiving mode. If valid FSK data received, the chip sends an interrupt to the microcontroller and continues filling the RX FIFO. After
the transmission is over and the FIFO is read out completely and all other interrupts are cleared, the chip goes back to low power
consumption mode.
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