PCF2129 datasheet(54/86 Pages) PHILIPS

54 / 86 page

PCF2129

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Product data sheet

Rev. 7 — 19 December 2014

54 of 86

NXP Semiconductors

PCF2129

Accurate RTC with integrated quartz crystal for industrial applications

9.2 I2C-bus interface

The I2C-bus is for bidirectional, two-line communication between different ICs or modules.

The two lines are a Serial DAta line (SDA) and a Serial CLock line (SCL). Both lines are

connected to a positive supply by a pull-up resistor. Data transfer is initiated only when the

bus is not busy.

9.2.1 Bit transfer

One data bit is transferred during each clock pulse. The data on the SDA line remains

stable during the HIGH period of the clock pulse as changes in the data line at this time

are interpreted as control signals (see Figure 33).

9.2.2 START and STOP conditions

Both data and clock lines remain HIGH when the bus is not busy. A HIGH-to-LOW

transition of the data line, while the clock is HIGH, is defined as the START condition S.

A LOW-to-HIGH transition of the data line while the clock is HIGH is defined as the STOP

condition P (see Figure 34).

Remark: For the PCF2129, a repeated START is not allowed. Therefore a STOP has to

be released before the next START.

9.2.3 System configuration

A device generating a message is a transmitter; a device receiving a message is the

receiver. The device that controls the message is the master; and the devices which are

controlled by the master are the slaves.

The PCF2129 can act as a slave transmitter and a slave receiver.

Fig 33. Bit transfer

Fig 34. Definition of START and STOP conditions

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