MFRC522 datasheet(17/96 Pages) NXP

17 / 96 page

MFRC522_33

Product data sheet

PUBLIC

Rev. 3 — 26 October 2009

112133

17 of 96

NXP Semiconductors

MFRC522

Contactless reader IC

8.1.4.4

Acknowledge

An acknowledge must be sent at the end of one data byte. 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 pulls 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 indicates 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

releases the data line to allow the master to generate a STOP (P) or repeated START (Sr)

condition.

Fig 14. Acknowledge on the I2C-bus

mbc602

START

condition

clock pulse for

acknowledgement

not acknowledge

acknowledge

data output

by transmitter

data output

by receiver

SCL from

master

Fig 15. Data transfer on the I2C-bus

msc608

SDA

SCL

STOP or

repeated START

condition

START or

repeated START

condition

3 - 8

ACK

MSB

acknowledgement

signal from slave

byte complete,

interrupt within slave

clock line held LOW while

interrupts are serviced

acknowledgement

signal from receiver

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