RC522 datasheet(54/109 Pages) NXP

54 / 109 page

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Product data sheet

Rev. 3.2 — 22 May 2007

54 of 109

NXP Semiconductors

MFRC522

Contactless Reader IC

10.4.4 Byte format

Each byte has to be followed by an acknowledge bit. Data is transferred with the MSB

first, see Figure 16 “First byte following the START procedure.”. The number of

transmitted bytes during one data transfer is unrestricted but shall fulfil the read/ write

cycle format.

10.4.5 Acknowledge

An acknowledge at the end of one data byte is mandatory. The acknowledge-related clock

pulse is generated by the master. The transmitter of data, either master or slave, releases

the SDA line (HIGH) during the acknowledge clock pulse. The receiver shall pull down the

SDA line during the acknowledge clock pulse so that it remains stable LOW during the

HIGH period of this clock pulse.

The master can then generate either a STOP (P) condition to stop the transfer, or a

repeated START (Sr) condition to start a new transfer.

A master-receiver shall indicate the end of data to the slave- transmitter by not generating

an acknowledge on the last byte that was clocked out by the slave. The slave-transmitter

shall release the data line to allow the master to generate a STOP (P) or repeated START

(Sr) condition.

Fig 14. Acknowledge on the I2C- bus.

RC522 Datasheet(PDF) 54 Page - NXP Semiconductors