LP55271 datasheet(15/21 Pages) NSC

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2C Compatible Interface

2C SIGNALS

The SCL pin is used for the I

2C clock and the SDA pin is

used for bidirectional data transfer. Both these signals need

a pull-up resistor according to I

2C specification. The values

of the pull-up resistors are determined by the capacitance of

the bus (typ. ~1.8 k

Ω). Signal timing specifications are

shown in table I

2C Timing Parameters.

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.

20202449

2C Signals: Data Validity

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.

20202450

2C Start and Stop Conditions

TRANSFERRING DATA

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

the most significant bit (MSB) being transferred first. 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 receiver must pull down the

SDA line during the 9

th clock pulse, signifying an acknowl-

edge. A receiver which has been addressed must generate

an acknowledge after each byte has been received.

After the START condition, the I

2C master sends a chip

address. This address is seven bits long followed by an

eighth bit which is a data direction bit (R/W). The LP55271

address is 4C hex. 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.

When a READ function is to be accomplished, a WRITE

function must precede the READ function, as shown in the

2C Read Cycle waveform.

20202451

2C Chip Address 4C hex for LP55271

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