PCF85063TP All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 4 — 6 May 2015 23 of 52
NXP Semiconductors
PCF85063TP
Tiny Real-Time Clock/calendar
9. Characteristics of the I
2
C-bus interface
The I
2
C-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 must
be connected to a positive supply via a pull-up resistor. Data transfer may be initiated only
when the bus is not busy.
9.1 Bit transfer
One data bit is transferred during each clock pulse. The data on the SDA line must remain
stable during the HIGH period of the clock pulse, as changes in the data line at this time
are interpreted as a control signal (see Figure 13
).
9.2 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 14
).
9.3 System configuration
A device generating a message is a transmitter; a device receiving a message is a
receiver. The device that controls the message is the master; and the devices which are
controlled by the master are the slaves (see Figure 15
).
Fig 13. Bit transfer
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Fig 14. Definition of START and STOP conditions
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