RFM02 Datasheet, PDF (3/24 Pages) List of Unclassifed Manufacturers – Universal ISM Band FSK Transmitter

RFM02
Crystal Oscillator
The chip has a single-pin crystal oscillator circuit, which provides a 10 MHz reference signal for the
PLL. To reduce external parts and simplify design, the crystal load capacitor is internal and
programmable. Guidelines for selecting the appropriate crystal can be found later in this datasheet.
The transmitters can supply the clock signal for the microcontroller, so accurate timing is possible
without the need for a second crystal. When the chip receives a Sleep Command from the microcontroller
and turns itself off, it provides several further clock pulses (“clock tail”) for the microcontroller to be able to
go to idle or sleep mode. The length of the clock tail is programmable.
Low Battery Voltage Detector
The low battery voltage detector circuit monitors the supply voltage and generates an interrupt if it
falls below a programmable threshold level.
Wake-Up Timer
The wake-up timer has very low current consumption (1.5 uA typical) and can be programmed from
1 ms to several days with an accuracy of ±5%.
It calibrates itself to the crystal oscillator at every startup, and then every 30 seconds. When the
oscillator is switched off, the calibration circuit switches on the crystal oscillator only long enough for a
quick calibration (a few milliseconds) to facilitate accurate wake-up timing.
Event Handling
In order to minimize current consumption, the device supports sleep mode. Active mode can be
initiated by several wake-up events: timeout of wake-up timer, detection of low supply voltage or through
the serial interface.
If any wake-up event occurs, the wake-up logic generates an interrupt, which can be used to wake
up the microcontroller, effectively reducing the period the microcontroller has to be active. The cause
of the interrupt can be read out from the transmitters by the microcontroller through the nIRQ pin.
Interface
An SPI compatible serial interface lets the user select the operating frequency band and center
frequency of the synthesizer, polarity and deviation of FSK modulation, and output power level.
Division ratio for the microcontroller clock, wake-up timer period, and low battery detector threshold
are also programmable. Any of these auxiliary functions can be disabled when not needed. All
parameters are set to default after power-on; the programmed values are retained during sleep mode.
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