CR14 datasheet(9/46 Pages) STMICROELECTRONICS

9 / 46 page

CR14

2 Signal description

9/46

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 (RFOUT)

The Antenna Output Driver pin, RFOUT, generates the modulated 13.56MHz signal on the

antenna. Care must be taken as it will not withstand a short-circuit.

RFOUT 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 RFOUT pin and GND.

2.3

Antenna Input Filter (RFIN)

The antenna input filter of the CR14, RFIN, 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 (VREF)

The Transmitter Reference Voltage input, VREF, 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 VCC. (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.

CR14 Datasheet(PDF) 9 Page - STMicroelectronics