RC522 datasheet(57/109 Pages) NXP

57 / 109 page

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Product data sheet

Rev. 3.2 — 22 May 2007

57 of 109

NXP Semiconductors

MFRC522

Contactless Reader IC

10.4.8 Register Read Access

To read out data from a specific register address of the MFRC522 the host controller shall

use the procedure:

First a write access to the specific register address has to be performed as indicated in the

following frame.

The first byte of a frame indicates the device address according to the I2C rules. The

second byte indicates the register address. No data bytes are added.

The read/write bit shall be 0.

Having performed this write access, the read access can start. The host has to send the

device address of the MFRC522. As an answer to this the MFRC522 responds with the

content of this register. In one frame all n-data bytes could be read from the same register

address. This enables for example a fast FIFO access or register polling.

The read/write bit shall be set to logic 1.

Fig 17. Register Read and Write Access

Write Cycle

Read Cycle

I2C slave address

A7-A0

(W)

Ack

Joiner register

address A5-A0

Ack

DATA

[7..0]

[0..n]

Ack

I2C slave address

A7-A0

(W)

Ack

Joiner register

address A5-A0

Ack

I2C slave address

A7-A0

(R)

Ack

DATA

[7..0]

0..n

Ack

[0..n]

DATA

[7..0]

Nack

sent by master

sent by slave

start condition

stop condition

ACK

acknowledge

Nack

not acknowlege

(W)

write cycle

(R)

read cycle

Optional, if the previous access was on the same register address

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