CR14 Datasheet, PDF (9/46 Pages) STMicroelectronics – Low Cost ISO14443 type-B Contactless Coupler Chip with Anti-Collision and CRC Management

CR14
2 Signal description
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 CR14, 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: CR14 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 CR14, 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 CR14. 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.
9/46