【NXP】 Basic introduction to PCF7991 chip

I. Foreword

       This article mainly introduces the basic information and characteristics of NXP PCF7991, introduces the communication commands and communication timing between MCU and PCF7991, and writes data through the write command, and then reads out the configured parameter set through the read command to verify the successful communication between MCU and PCF7991.

1. Basic introduction

1. overview

       PCF7991AT is a fully integrated advanced base station integrated circuit ABIC (Advanced Basestation IC), designed for automobile engine anti-theft systems, providing read and write access to the ID transponders. The device is designed to use transponders that operate at 125KHz and use ASK to write and AM/PM to read. The amplifier gain, filter cut-off frequency, etc. can be optimized according to the needs of the system and the transponders.

       The PCF7991AT is designed for easy integration into the engine's internal read-write or read-only system, characterized by a high degree of integration and a very small number of external components. The device integrates a powerful antenna driver/modulator, a low-noise adaptive sampling time demodulator, a programmable filter/amplifier, and a digital converter, which is suitable for base stations that need to be designed with high performance. PCF7991AT can communicate in both directions with the transponders. By connecting DIN and DOUT, the three-wire interface can be configured to operate as a two-wire interface.

2. Features and applications

2.1 Features

• Fully integrated single-chip base station

• Integrated powerful programmable antenna driver/modulator

• On-chip clock oscillator and divider in the case of external clock reference

• Antenna open circuit and short circuit detection

• Low-power and ultra-low-power standby modes

• Less external components and small packaging

2.2 Application

     The advancement of semiconductor technology has provided automobile manufacturers with intelligent, safer and more convenient automotive technology. PCF7991 is suitable for reading and writing operations and has a stable frequency. This chip is used as an RFID front-end circuit to successfully apply RFID electronic tag technology to automobile electronic locks. Through the 125KHz wireless connection between the car and the key, the RFID electronic tag technology is successfully applied to automobile electronic locks.Communication to achieve electronic identification.


3.  Introduction to the main function pins

4.   Minimum application circuit

        The figure shows the minimum application circuit of PCF7991AT. The antenna coil La and the capacitor Ca form a series resonant LC circuit (f=125KHz). The capacitors in QGND and CEXT play a role in providing the device's internal bias and decoupling.

2. PCF7991AT communication

1. PCF7991AT communication overview

       The communication between PCF7991AT and MCU is done by a three-wire digital interface. This interface is used in transparent mode (READ_TAG, WRITE_TAG / WRITE_TAG_N) in order to read and write device configuration data. Before sending the command, the PCF7991AT needs to initialize the serial interface to communicate with the MCU. The initialization condition is: when SCLK is high, the DIN signal needs a transition from low to high. All commands transmitted to the PCF7991AT serial interface are transmitted starting from the most significant bit. When SCLK is high, DIN is latched and DOUT is valid. The digital filter is based on the rate of 1/fTX (8 µs standard value) provided by the sampling SCLK and DIN inputs, and the state changes of the DIN inputs are delayed by 16 to 24 µs until they are recognized by the internal circuit.

2. PCF7991AT communication send command set

2.1 GET_SAMPLING_TIME command

       This command is used to read back the setting of the sampling time TS.

2.2 GET_CONFIG_PAGE command

       This command is used to read back the parameter sets configured on PAGE 0, PAGE 1, PAGE 2, and PAGE 3, and read back the programmed transmitter pulse width.

2.3 READ_PHASE command

       This command is used to read the phase TANT (binary bit0~ bit5) of the antenna, which is measured in each carrier cycle.

2.4 READ_TAG command

       This command is used to read the demodulated bit stream from the transponders. After the three command bits are completed, PCF7991 immediately switches to READ_TAG mode, and the READ_TAG mode is terminated by the SCLK low-to-high transition signal.

       This command is used to write data to the transponder and set the parameters of the modulator blanking.

       If N3-N0 is set to 0, the signal on DIN will be switched to the driver in a transparent manner. If N3-N0 is set to 1～1111, the time interval between the driver and the closed state is equal to N*T0 (T0=8 µs)

       The WRITE_TAG mode is terminated by the SCLK low-to-high transition signal, so regardless of the activation state of the modulation pulse timer, the drivers will restart their initial state.

       A high level on DIN is equivalent to the antenna drive turned off, and a low level is equivalent to the antenna drive turned on.

2.6 WRITE_TAG command

       This is the 3-digit simple format of the WRITE_TAG_N command. It allows to switch to WRITE_TAG mode with minimal communication time. The WRITE_TAG mode is also terminated by the SCLK low-to-high transition signal, so regardless of the activation state of the modulation pulse timer, the drivers will restart their initial state.

2.7 SET_SAMPLING_TIME command

       This command specifies the sampling time TS of the modulator, and the sampling time is binary encoded.

2.8 SET_CONFIG_STAGE command

       This command is used to configure the receiver parameter table (cutoff frequency, gain factor) and different operating modes.

 

3. PCF7991AT communication debugging

1. Serial port communication and timing are simulated through the IO port and delay. After the initialization condition SCLK is pulled high and maintained at a high level, the transition from low level to high level begins after DIN is pulled low from a high level. The stable period of SCLK is 16 µs (keep 8 µs low and 8 µs high level).

2. SCLK is collected from the rising edge, and the first edge is maintained after the initialization is maintained at a high level. Data is sent by changing the DIN level + a delay + SCLK transitions from low to high to collect DIN data + a delay + an empty instruction + a delay + SCLK byHigh-to-low transition + a delay, and so on.

3. Reading the response is also through SCLK to periodically read the level of the DOUT IO port to obtain the response data. Write data to PAGE 0 through the SET_CONFIG_ PAGE command, and read the data written to PAGE 0 through the GET_CONFIG_ PAGE command, verify the communication is successful through comparison, and write the data to PCF7991.

The SET_CONFIG_STAGE command writes to D3 D2 D1 D0 ：

The GET_CONFIG_STAGE command reads D3 D2 D1 D0 ：


四、参考资料

        【S32K 开发指南】LPSPI 模块介绍与例程建立

                        https://www.wpgdadatong.com/blog/detail?BID=B1546

       【PCF7991AT DataSheet. pdf】

                       https://wenku.baidu.com/view/7ed6c243a8956bec0975e334.html