RC522-I2C/UART module

I bought a POS machine from Laowang Electronics next door for two yuan and a half. When I took it apart, there was a lithium battery, a screen, and a buzzer. There was no data on the main control, and there was no data on the Bluetooth chip. The silk screen of the NFC chip was worn away. I guessed that the NFC is MFRC522. After comparing the wiring and the data sheet, I found that the pins of the antenna part were the same, so I removed it and soldered it to the RC522 module. I guessed it right!

View data sheet: https://www.semiee.com/file/backup/NXP-MFRC522.pdf

Communication mode

Through the Datasheet, I learned that MFRC522 can support 3 communication methods: UART, SPI, and I2C.

1. When the I2C pin is high, the chip works in I2C mode. At this time, the EA pin is used to set the I2C custom address to 3bit or 7bit. When EA=1, the chip address is [0] [ADR_5~ADR_0] ;When EA=0, the chip address is [0101] [ADR_2~ADR_0].

2. When the I2C pin is low level, the chip works in UART or SPI mode. At this time, EA=0, selects UART mode, and EA=1, selects SPI mode.

circuit

Since the UART and I2C pins are the same, it can be directly made into a UART and I2C multiplexing module. Connect the EA pin to low level and use the I2C pin to select UART or I2C.

Select I2C or UART mode through R1 and R2.

PCB design

Select UART or I2C mode by soldering R1 or R2 on the PCB. You can see on the back of the PCB that the UART and I2C pins are multiplexed.

Among them, U1, L1, L2, and X1 are removed from the POS machine.

NFC coil under white box

test

Passed the test using Arduino+MF522_I2C library

Read card information