LP3972 datasheet(21/59 Pages) NSC

21 / 59 page

2C Compatible Interface

2C DATA VALIDITY

The data on SDA line must be stable during the HIGH period

of the clock signal (SCL). In other words, state of the data

line can only be changed when CLK is LOW.

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2C START and STOP CONDITIONS

START and STOP bits classify the beginning and the end of

the I

2C session. START condition is defined as SDA signal

transitioning from HIGH to LOW while SCL line is HIGH.

STOP condition is defined as the SDA transitioning from

LOW to HIGH while SCL is HIGH. The I

2C master always

generates START and STOP bits. The I

2C bus is considered

to be busy after START condition and free after STOP con-

dition. During data transmission, I

2C master can generate

repeated START conditions. First START and repeated

START conditions are equivalent, function-wise.

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TRANSFERRING DATA

Every byte put on the SDA line must be eight bits long, with

the most significant bit (MSB) being transferred first. The

number of bytes that can be transmitted per transfer is

unrestricted. Each byte of data has to be followed by an

acknowledge bit. The acknowledge related clock pulse is

generated by the master. The transmitter releases the SDA

line (HIGH) during the acknowledge clock pulse. The re-

ceiver must pull down the SDA line during the 9th clock

pulse, signifying an acknowledge. A receiver which has been

addressed must generate an acknowledge after each byte

has been received.

After the START condition, a chip address is sent by the I

master. This address is seven bits long followed by an eighth

bit which is a data direction bit (R/W). The LP3972 address

is 34h. For the eighth bit, a “0” indicates a WRITE and a “1”

indicates a READ. The second byte selects the register to

which the data will be written. The third byte contains data to

write to the selected register.

2C CHIP ADDRESS - 7h’34

MSB

ADR6

Bit7

ADR5

Bit6

ADR4

Bit5

ADR3

Bit4

ADR2

Bit3

ADR1

Bit2

ADR0

Bit1

R/W

Bit0

0110100

R/W

LP3972 数据表(PDF) 21 Page - National Semiconductor (TI)

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