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CRX14 Datasheet(PDF) 7 Page - STMicroelectronics |
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CRX14 Datasheet(HTML) 7 Page - STMicroelectronics |
7 / 40 page 7/40 CRX14 SIGNAL DESCRIPTION See Figure 2., and Table 1., for an overview of the signals connected to this device. Oscillator (OSC1, OSC2). The OSC1 and OSC2 pins are internally connected to the on-chip oscil- lator 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 exter- nal clock is used, it must be connected to OSC1 and OSC2 must be left open. Antenna Output Driver (RFOUT). The Antenna Output Driver pin, RFOUT, generates the modulat- ed 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 circuit- ry as shown in Figure 5. The LRC antenna circuitry must be connected across the RFOUT pin and GND. Antenna Input Filter (RFIN). The antenna input filter of the CRX14, RFIN, has to be connected to the external antenna through an adapter circuit, as shown in Figure 5. 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. Transmitter Reference Voltage (VREF). The Transmitter Reference Voltage input, VREF, pro- vides 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 5. Serial Clock (SCL). The SCL input pin is used to strobe all I²C data in and out of the CRX14. In ap- plications where this line is used by slave devices to synchronize the bus to a slower clock, the mas- ter must have an open drain output, and a pull-up resistor must be connected from the Serial Clock (SCL) to VCC. ( Figure 6. indicates how the value of the pull-up resistor can be calculated). In most applications, though, this method of syn- chronization 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. Serial Data (SDA). The SDA signal is bi-direc- tional. It is used to transfer I²C data in and out of the CRX14. It is an open drain output that may be wire-OR’ed with other open drain or open collector signals on the bus. A pull-up resistor must be con- nected from Serial data (SDA) to VCC. (Figure 6. indicates how the value of the pull-up resistor can be calculated). Chip Enable (E0, E1, E2). The Chip Enable in- puts E0, E1, E2 are used to set and reset the value on the three least significant bits (b3, b2, b1) of the 7-bit I²C Device Select Code. They are used for hardwired addressing, allowing up to eight CRX14 devices to be addressed on the same I²C bus. These inputs may be driven dynamically or tied to VCC or GND to establish the Device Select Code (note that the VIL and VIH levels for the inputs are CMOS compatible, not TTL compatible). When left open, E0, E1 and E2 are internally read at the logic level 0 due to the internal pull-down re- sistors connected to each inputs. Power Supply (VCC, GND, GND_RF). Power is supplied to the CRX14 using the VCC, GND and GND_RF pins. VCC is the Power Supply pin that supplies the pow- er (+5V) for all CRX14 operations. The GND and GND_RF pins are ground connec- tions. They must be connected together. Decoupling capacitors should be connected be- tween the VCC Supply Voltage pin, the GND Ground pin and the GND_REF Ground pin to filter the power line, as shown in Figure 5. |
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