Datasheet
start
MSB Chip Address LSB w
ack
MSB Register 0x02h LSB
ack
MSB Data LSB
ack
stop
ack from slave
ack from slave ack from slave
SCL
SDA
start
slave address =
0011010
2
w ack
register address = 0x02h
ack ack
register 0x02h data
stop
ADR6
Bit7
ADR5
bit6
ADR4
bit5
ADR3
bit4
ADR2
bit3
ADR1
bit2
ADR0
bit1
R/W
bit0
MSB LSB
I
2
C SLAVE address (chip address)
SDA
SCL
S
P
START condition
STOP condition
LMV1089
www.ti.com
SNAS441H –SEPTEMBER 2008–REVISED MAY 2010
The master should issue STOP after no acknowledgment.
Figure 24. I
2
C Start 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 acknowledge (ACK). A receiver which has
been addressed must generate an acknowledge after each byte has been received.
After the START condition, the I
2
C 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 LMV1089 address is 11001100
2
or 11001110
2
. 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.
Figure 25. I
2
C Chip Address
Register changes take effect at the SCL rising edge during the last ACK from slave.
In Figure 26, a write example is shown, for a device with a randomly chosen address'00110100
2
'.
w = write (SDA = “0”)
r = read (SDA = “1”)
ack = acknowledge (SDA pulled down by slave)
rs = repeated start
Figure 26. Example I
2
C Write Cycle
When a READ function is to be accomplished, a WRITE function must precede the READ function, as shown in
the Read Cycle waveform. Figure 27 shows this read example for a randomly chosen address'00110101
2
.
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