MFRC522 datasheet(55/109 Pages) NXP

55 / 109 page

112132

Product data sheet

Rev. 3.2 — 22 May 2007

55 of 109

NXP Semiconductors

MFRC522

Contactless Reader IC

10.4.6 7-BIT ADDRESSING

During the I2C-bus addressing procedure, the first byte after the START condition is used

to determine which slave will be selected by the master.

As an exception several address numbers are reserved. During device configuration, the

designer has to ensure, that no collision with these reserved addresses is possible. Check

the corresponding I2C specification for a complete list of reserved addresses.

The I2C address specification is dependent on the definition of the EA Pin. Immediately

after releasing the reset pin or after power on reset, the device defines the I2C address

according EA pin.

If EA Pin is set to LOW than for all MFRC522 devices the upper 4 bits of the device bus

address are reserved by NXP and set to 0101(bin). The remaining 3 bits (ADR_0, ADR_1,

ADR_2) of the Slave Address can freely configured by the customer in order to prevent

collisions with other I2C devices.

If EA Pin is set to HIGH than ADR_0 to ADR_5 can be completely specified at the external

pins according to Table Table 135 “Connection Scheme for detecting the different

Interface Types”. ADR_6 is always set to logic 0.

In both modes, the external address coding is latched immediately after releasing the

reset condition. Further changes at the used pins are not taken into consideration.

Depending on the external wiring, the I2C address pins could be used for test signal

output.

Fig 15. Data transfer on the I2C- bus.

MFRC522 Datasheet(PDF) 55 Page - NXP Semiconductors