MFRC522 datasheet(19/96 Pages) NXP

19 / 96 page

MFRC522_33

Product data sheet

PUBLIC

Rev. 3 — 26 October 2009

112133

19 of 96

NXP Semiconductors

MFRC522

Contactless reader IC

8.1.4.7

To read out data from a speciﬁc register address in the MFRC522, the host controller must

use the following procedure:

• Firstly, a write access to the speciﬁc register address must be performed as indicated

in the frame that follows

• The ﬁrst byte of a frame indicates the device address according to the I2C-bus rules

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

• The Read/Write bit is 0

After the write access, read access can start. The host sends the device address of the

MFRC522. In response, the MFRC522 sends the content of the read access register. In

one frame all data bytes can be read from the same register address. This enables fast

FIFO buffer access or register polling.

The Read/Write (R/W) bit is set to logic 1.

Fig 17. Register read and write access

001aak592

I2C-BUS

SLAVE ADDRESS

[A7:A0]

JOINER REGISTER

ADDRESS [A5:A0]

write cycle

(W)

DATA

[7:0]

[0:n]

I2C-BUS

SLAVE ADDRESS

[A7:A0]

JOINER REGISTER

ADDRESS [A5:A0]

read cycle

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

(W)

start condition

stop condition

acknowledge

not acknowledge

write cycle

read cycle

I2C-BUS

SLAVE ADDRESS

[A7:A0]

sent by master

sent by slave

DATA

[7:0]

(R)

DATA

[7:0]

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