ATmega88 datasheet(203/340 Pages) ATMEL

203 / 340 page

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7530H–AVR–02/09

ATmega48/88/168 Automotive

Figure 19-2. Data Validity

19.3.2

START and STOP Conditions

The Master initiates and terminates a data transmission. The transmission is initiated when the

Master issues a START condition on the bus, and it is terminated when the Master issues a

STOP condition. Between a START and a STOP condition, the bus is considered busy, and no

other master should try to seize control of the bus. A special case occurs when a new START

condition is issued between a START and STOP condition. This is referred to as a REPEATED

START condition, and is used when the Master wishes to initiate a new transfer without relin-

quishing control of the bus. After a REPEATED START, the bus is considered busy until the next

STOP. This is identical to the START behavior, and therefore START is used to describe both

START and REPEATED START for the remainder of this datasheet, unless otherwise noted. As

depicted below, START and STOP conditions are signalled by changing the level of the SDA

line when the SCL line is high.

Figure 19-3. START, REPEATED START and STOP conditions

SDA

SCL

Data Stable

Data Change

SDA

SCL

START

STOP

REPEATED START

STOP

START

ATmega88 Datasheet(PDF) 203 Page - ATMEL Corporation