RFM68CW
RFM68CW
6.2. NRESET Pin
When required, the pin NRESET can be controlled externally, to allow for:
either a delayed Power On Reset (POR) cycle of the RFM68CW, allowing for the companion micro to reset and
assign its
port directions. This is achieved by connecting a R/C time constant to the NRESET pin.
or an On-the-go Reset of the RFM68CW at any moment in time, if required by the application. This is achieved by
pulling
the NRESET pin low for more than 100 microseconds, then releasing it to high impedance (normal termination).
6.3. TX_READY Pin
For timing critical applications, TX_READY pin can be useful to know precisely when the transmitter is ready for operation,
and therefore save energy. To this end, TX_READY can optionally be connected to inform the companion device that the
PA ramp up phase has been terminated, hence the RFM68CW is ready for data transmission.
6.4. Low Power Optimization
The RFM68CW is designed to reduce the cost of the RF transmitter functionnality. To this end, a single DATA signal can
be enough to operate the transmitter, in any of the two Power & Go modes. In this situation, TS_START and TOFFT
timings, tabulated in Section 2.4, must be respected, leading to significant periods of time during which the transmitter is On
and no valuable information is transmitted.
For more demanding applications where energy usage is critical, the RFM68CW offers hardware and software support to
accurately control the transmitter On time, and therefore save energy:
6.4.1. 2 Connections: CTRL, DATA
If the two signals of the TWI interface can be controlled by the host microcontroller, Tx On time can be accurately controlled
as follows:
At the device turn on, instead of waiting for TS_TR (2ms max, but very XTAL dependant), the status flag
TX_READY
can be polled on the TWI interface. As soon as the TX_READY flag is set, the microcontroller can start toggling DATA
to transmit the useful packet. This method is valid in both Forced Tx and Automatic modes.
At the device turn off, instead of waiting for TOFFT (2 or 20ms), the user can immediately turn off the transmitter
after
the transmission of packet, assuming that the Forced Transmit mode was selected.
6.4.2. 3 Connections: CTRL, DATA, TX_READY
In applications where the number of connections between the microcontroller and the RF module is less critical,
TX_READY pin can be connected to either a GPIO port, or an external interrupt port of the micro. The two optimizations
described in the former subsection will also be possibl
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