PCF8523 datasheet(44/66 Pages) NXP

44 / 66 page

PCF8523

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Product data sheet

Rev. 3 — 30 March 2011

44 of 66

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

The PCF8523 can act as a slave transmitter and a slave receiver.

8.11.4 Acknowledge

The number of data bytes transferred between the START and STOP conditions from

transmitter to receiver is unlimited. Each byte of eight bits is followed by an acknowledge

cycle.

• A slave receiver, which is addressed, must generate an acknowledge cycle after the

reception of each byte.

• Also a master receiver must generate an acknowledge cycle after the reception of

each byte that has been clocked out of the slave transmitter.

• The device that acknowledges must pull-down the SDA line during the acknowledge

clock pulse, so that the SDA line is stable LOW during the HIGH period of the related

acknowledge clock pulse (set-up and hold times must be taken into consideration).

• A master receiver must signal an end of data to the transmitter by not generating an

acknowledge cycle on the last byte that has been clocked out of the slave. In this

event, the transmitter must leave the data line HIGH to enable the master to generate

a STOP condition.

Acknowledgement on the I2C-bus is shown in Figure 30.

Fig 29. System configuration

mba605

MASTER

TRANSMITTER

RECEIVER

SLAVE

RECEIVER

SLAVE

TRANSMITTER

RECEIVER

MASTER

TRANSMITTER

MASTER

TRANSMITTER

RECEIVER

SDA

SCL

Fig 30. Acknowledgement 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

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