PN7120 does not respond on the I2C bus

NXP’s PN7120 is NFC controller for contactless communication at 13.56MHz. It interfaces with the host CPU via the I2C bus. The I2C slave address of  PN7120 is 0b010100Lx, where L is a configurable LSB of the address (by pin B2, I2CADDR0), and x is the standard I2C R/W bit. Hence the normal I2C address is either 0x28 or 0x29:

// write to device at address 0x28, R/W=Write
i2c_master_write_byte(cmd, (0x28 << 1) | WRITE_BIT, ACK_CHECK_EN);

According to UM10819 User Manual, Fig. 23 on page 35, the first NCI command after reset must be the CORE_RESET_CMD, which is followed by an appropriate response from PN7120.

The CORE_RESET_CMD is simply this byte sequence:

const uint8_t nci_core_reset_cmd[] = { 0x20, 0x00, 0x01, 0x01 };

What they don’t tell us in the datasheet (or else I could not find it): there is a boot timeout cca 990ms after the reset is removed (pin VEN=1) within which the CORE_RESET_CMD must be recevied. If it is not received, the PN7120 goes in a strange power-down mode and will no longer respond on the I2C bus! Only a new hw reset via VEN can bring it out of the power-down.

This picture provides updated boot state diagram of PN7120:


CORE_RESET_CMD on the I2C bus:

Simply no repospone on I2C address 0x28 if there was no CORE_RESET_CMD within 990ms after PN7120 reset:

Our hardware: ESP32 and Mikroelektronika’s NFC Click.


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