LM3535 datasheet(12/26 Pages) NSC

12 / 26 page

smaller pull-up results in higher switching currents with faster

edges.

START AND STOP CONDITIONS

START and STOP conditions classify the beginning and the

end of the I2C session. A START condition is defined as SDIO

signal transitioning from HIGH to LOW while SCL line is

HIGH. A STOP condition is defined as the SDIO transitioning

from LOW to HIGH while SCL is HIGH. The I2C master always

generates START and STOP conditions. The I2C bus is con-

sidered to be busy after a START condition and free after a

STOP condition. During data transmission, the I2C master

can generate repeated START conditions. First START and

repeated START conditions are equivalent, function-wise.

30082411

FIGURE 2. Start and Stop Conditions

TRANSFERRING DATA

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

the most significant bit (MSB) transferred first. Each byte of

data has to be followed by an acknowledge bit. The acknowl-

edge related clock pulse is generated by the master. The

master releases the SDIO line (HIGH) during the acknowl-

edge clock pulse. The LM3535 pulls down the SDIO line

during the 9th clock pulse, signifying an acknowledge. The

LM3535 generates an acknowledge after each byte is re-

ceived. There is no acknowledge created after data is read

from the LM3535.

After the START condition, the I2C master sends a chip ad-

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

bit which is a data direction bit (R/W). The LM3535 7-bit ad-

dress is 38h. 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.

30082412

FIGURE 3. Write Cycle

w = write (SDIO = "0")

r = read (SDIO = "1")

ack = acknowledge (SDIO pulled down by either master or slave)

id = chip address, 38h for LM3535

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