RFHCS362F Datasheet, PDF (35/60 Pages) Microchip Technology – Code Hopping Encoder with UHF ASK/FSK Transmitter

6.7 Mode Control Logic
The mode control logic pin RFENIN controls the oper-
ation of the transmitter (Table 6-7). When RFENIN
goes high, the crystal oscillator starts up. The voltage
on the LF pin ramps up proportionally to the RF fre-
quency. The PLL can lock onto the frequency faster
than the starting up crystal can stabilize. When the LF
pin reaches 0.8V, the RF frequency is close to locked
on the crystal frequency. This initiates a 150 micro-
second delay to ensure that the PLL settles. After the
delay, the PS/DATAASK bias current and power ampli-
fier are enabled to start transmitting.
When RFENIN goes low, the transmitter goes into low
power Standby mode. The power amplifier is dis-
abled, the crystal oscillator stops, and the PS/
DATAASK pin is driven low. This will be a conflict if other
circuitry drives the PS/DATAASK pin high while RFENIN
is low. The encoder DATA pin is typically the only con-
nection to PS/DATAASK and it always drives DATA low
before RFENOUT goes low.
For most applications the RFENIN pin is connected
directly to the RFENOUT pin. The RFENIN pin has an
internal pull-down resistor.
TABLE 6-7: RFENIN PIN STATES
RFEN
0
1
Description
Transmitter and CLKOUT in Standby
Transmitter and CLKOUT enabled
rfHCS362G/362F
© 2002 Microchip Technology Inc.
Preliminary
DS41189A-page 35