PCF2129AT datasheet(55/86 Pages) PHILIPS

55 / 86 page

PCF2129

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Product data sheet

Rev. 7 — 19 December 2014

55 of 86

NXP Semiconductors

PCF2129

Accurate RTC with integrated quartz crystal for industrial applications

9.2.4 Acknowledge

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

transmitter to receiver is unlimited. Each byte of 8 bits is followed by an acknowledge

cycle.

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

reception of each byte.

• Also a master receiver must generate an acknowledge 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

acknowledge related clock pulse (set-up and hold times must be considered).

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

acknowledge 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 illustrated in Figure 36.

9.2.5 I2C-bus protocol

After a start condition, a valid hardware address has to be sent to a PCF2129 device. The

appropriate I2C-bus slave address is 1010001. The entire I2C-bus slave address byte is

shown in Table 77.

Fig 35. System configuration

Fig 36. Acknowledgement on the I2C-bus

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