LP8556 datasheet(29/63 Pages) TI1

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SDA

SCL

Start

Condition

Stop

Condition

SCL

3 - 6

Start

Condition

Acknowledgment

Signal From Receiver

Data Output

Receiver

Data Output

Transmitter

Transmitter Stays Off the

Bus During the

Acknowledgment Clock

LP8556

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SNVS871I – JULY 2012 – REVISED MARCH 2016

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Programming (continued)

Figure 14. Start and Stop

The Master device on the bus always generates the Start and Stop Conditions (control codes). After a Start

Condition is generated, the bus is considered busy and it retains this status until a certain time after a Stop

Condition is generated. A high-to-low transition of the data line (SDA) while the clock (SCL) is high indicates a

Start Condition. A low-to-high transition of the SDA line while the SCL is high indicates a Stop Condition.

Figure 15. Start and Stop Conditions

In addition to the first Start Condition, a repeated Start Condition can be generated in the middle of a transaction.

This allows another device to be accessed, or a register read cycle.

8.5.1.3 Acknowledge Cycle

The Acknowledge Cycle consists of two signals: the acknowledge clock pulse the master sends with each byte

transferred, and the acknowledge signal sent by the receiving device.

The master generates the acknowledge clock pulse on the ninth clock pulse of the byte transfer. The transmitter

releases the SDA line (permits it to go high) to allow the receiver to send the acknowledge signal. The receiver

must pull down the SDA line during the acknowledge clock pulse and ensure that SDA remains low during the

high period of the clock pulse, thus signaling the correct reception of the last data byte and its readiness to

receive the next byte.

8.5.1.4 Acknowledge After Every Byte Rule

The master generates an acknowledge clock pulse after each byte transfer. The receiver sends an acknowledge

signal after every byte received.

There is one exception to the acknowledge after every byte rule. When the master is the receiver, it must

indicate to the transmitter an end of data by not-acknowledging (“negative acknowledge”) the last byte clocked

out of the slave. This negative acknowledge still includes the acknowledge clock pulse (generated by the

master), but the SDA line is not pulled down.

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