ST25R95 datasheet(3/61 Pages) STMICROELECTRONICS

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1.2

Clock management

The ST25R95 incorporates two clock sources, a high frequency oscillator (HFO) and a low frequency oscillator

(LFO).

The HFO uses an external 27.12 MHz crystal to generate the internal system clock and the clock for the drivers to

generate the RF field.

The LFO uses an internal 32 kHz RC oscillator to generate a slow system clock for low power operation modes.

In card emulation mode, a built-in clock recovery block is available which recovers the clock from the external HF

field. This block can be selected instead of HFO by setting the ClkRec bit in the Protocol Select command.

1.3

Power supply

The ST25R95 has two power supply pins:

•

VPS: supply of digital and analog blocks

•

VPS_TX: direct supply of the driver stage

1.4

List of terms

Table 1. List of terms

Term

Meaning

AFE

Analog front end

DAC

Digital analog converter

FDT

Frame delay time

FWT

Frame waiting time

GND

Ground

HFO

High frequency oscillator

LFO

Low frequency oscillator

MCU

Microcontroller unit

MIFARE (1)

Communication protocol

NFC

Near field communication

RFID

Radio frequency identification

RFU

Reserved for future use

RWT

Response waiting time

SPI

Serial peripheral interface

Low frequency period

tREF

Reference time

WFE

Wait for event

1. MIFARE® and MIFARE® Classic are registered trademarks of NXP BV.

ST25R95

Clock management

DS12807 - Rev 4

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