Start Signal; Slave Address Transmission - NXP Semiconductors freescale KV4 Series Reference Manual

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Calling Address

Calling Address

45.5.1.1 START signal

The bus is free when no master device is engaging the bus (both SCL and SDA are high).

When the bus is free, a master may initiate communication by sending a START signal.

A START signal is defined as a high-to-low transition of SDA while SCL is high. This

signal denotes the beginning of a new data transfer—each data transfer might contain

several bytes of data—and brings all slaves out of their idle states.

Immediately after the START signal, the first byte of a data transfer is the slave address

transmitted by the master. This address is a 7-bit calling address followed by an R/W bit.

The R/W bit tells the slave the desired direction of data transfer.

• 1 = Read transfer: The slave transmits data to the master

• 0 = Write transfer: The master transmits data to the slave

Only the slave with a calling address that matches the one transmitted by the master

responds by sending an acknowledge bit. The slave sends the acknowledge bit by pulling

SDA low at the ninth clock.

Freescale Semiconductor, Inc.

Figure 45-14. I2C bus transmission signals

KV4x Reference Manual, Rev. 2, 02/2015

Chapter 45 Inter-Integrated Circuit (I2C)

New Calling Address