RFPIC12F675 Datasheet, PDF (54/136 Pages) Microchip Technology – FLASH-Based Microcontroller with ASK/FSK Transmitter

rfPIC12F675
9.9 Digital Control Signals
The mode control logic pin RFEN controls the
operation of the transmitter. When RFEN goes high,
the crystal oscillator starts up. The voltage on the LF
pin ramps up proportionally to the RF frequency. The
PLL can lock onto the frequency faster than the start-
ing up crystal can stabilize. When the LF pin reaches
0.8V, the RF frequency is close to locked on the crys-
tal frequency. This initiates a 150 microsecond delay
to ensure that the PLL settles. After the delay, the PS
bias current and power amplifier are enabled to start
transmitting when DATAASK goes high.
When RFEN is low, the transmitter goes into a very
low power Standby mode. The power amplifier is
disabled and the crystal oscillator stops. The RFEN
pin has an internal pull-down resistor.
9.10 Low Voltage Output Disable
The rfPIC12F675 transmitter has a built in low voltage
disable centered at about 1.85V. If the supply voltage
drops below this voltage the power amplifier is
disabled to prevent uncontrolled transmissions.
DS70091B-page 54
Preliminary
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