CRX14 Signal description
Doc ID 8880 Rev 4 9/47
2 Signal description
See Figure 1: Logic diagram, and Table 1: Signal names, for an overview of the signals
connected to this device.
2.1 Oscillator (OSC1, OSC2)
The OSC1 and OSC2 pins are internally connected to the on-chip oscillator circuit. The
OSC1 pin is the input pin, the OSC2 is the output pin. For correct operation of the CRX14, it
is required to connect a 13.56MHz quartz crystal across OSC1 and OSC2. If an external
clock is used, it must be connected to OSC1 and OSC2 must be left open.
2.2 Antenna output driver (RF
OUT
)
The Antenna Output Driver pin, RF
OUT
, generates the modulated 13.56MHz signal on the
antenna. Care must be taken as it will not withstand a short-circuit.
RF
OUT
has to be connected to the antenna circuitry as shown in Figure 4: CRX14
application schematic The LRC antenna circuitry must be connected across the RF
OUT
pin
and GND.
2.3 Antenna input filter (RF
IN
)
The antenna input filter of the CRX14, RF
IN
, has to be connected to the external antenna
through an adapter circuit, as shown in Figure 4.
The input filter demodulates the signal generated on the antenna by the load variation of the
PICC. The resulting signal is then decoded by the 847kHz BPSK decoder.
2.4 Transmitter reference voltage (V
REF
)
The Transmitter Reference Voltage input, V
REF
, provides a reference voltage used by the
output driver for ASK modulation.
The Transmitter Reference Voltage input should be connected to an external capacitor, as
shown in Figure 4.
2.5 Serial clock (SCL)
The SCL input pin is used to strobe all I²C data in and out of the CRX14. In applications
where this line is used by slave devices to synchronize the bus to a slower clock, the master
must have an open drain output, and a pull-up resistor must be connected from the Serial
Clock (SCL) to V
CC
. (Figure 5 indicates how the value of the pull-up resistor can be
calculated).
In most applications, though, this method of synchronization is not employed, and so the
pull-up resistor is not necessary, provided that the master has a push-pull (rather than open
drain) output.
