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SLEEP
SLEEP
RX
(20 ms)
XTAL
(310 us)
SLEEP
(800 ms)
TUNE
(300 us)
RX
(20 ms)
XTAL
(310 us)
TUNE
(300 us)
time
Figure 12. Preamble Wake-On Operation without Preamble Detected
If a valid preamble is received, the RX state is extended to RX EXT state which is long enough for more than 2 data packets
reception. A valid preamble means the preamble of the size (16-symbol in this example) defined on the RFPDK. Please note that
the preamble defined for the Rx device is not necessarily the entire preamble length that is transmitted by the Tx device.
SLEEP
SLEEP
(800 ms)
RX
(20 ms)
Wake on preamble
Data Packet
RX EXT
(200 ms)
XTAL
(310 us)
TUNE
(300 us)
Data Packet
time
Preamble
Figure 13. Preamble Wake-On Operation with Preamble Detected
In order to ensure that the preamble can be captured by the Rx, the RX EXT must be longer than the valid preamble which is
16-symbol.
SLEEP, XTAL, TUNE
RX EXT
RX
Preamble
time
SLEEP, XTAL, TUNE
RX
Data Packet Data Packet
Figure 14. The Transmitted Preamble Length
Also, as shown in the above figure, for the Tx device, the transmitted preamble length must be long enough to ensure the Rx
reception:
Preamble Length > RX + SLEEP + XTAL + TUNE + RX
The longer the transmitted preamble length is, the more power the Tx device consumes in each transmission. Therefore, this
example is suitable for the application where the Tx device does not send out data very often, and the Rx device is very sensitive
about the current consumption.
In most of the applications, it is recommended that the CMT2250A can be paired with the CMT2150A (Low-Cost 240 – 480 MHz
OOK Stand-Alone Transmitter with Encoder). However, since the maximum size of the preamble sent by CMT2150A is only
16-symbol, the size might not be long enough to fulfill the WOR timing requirement introduced above. In this case, it is suggested
to use the stand-alone transmitter CMT2110A (Low-Cost 240 – 480 MHz OOK Transmitter) with an external MCU to pair with the
