ack

w

ack

rs

r

ack

ack stop

start

msb Chip Address lsb

msb Register Add lsb

msb Chip Address lsb

msb

DATA

lsb

ack from slave

SC

L

SD

A

ack from slave

ack from slave

ack from master

data from slave

repeated start

star

t

w

ac

k

addr =

h'00

ac

k

r

s

r

ac

k

address h'00

data

ac

k

sto

p

id = h'xx

id = h'xx

ack

w

ack

ack

stop

start

msb Chip Address lsb

msb Register Add lsb

msb

DATA

lsb

ack from slave

SCL

SDA

start

w ack

id = h'xx

addr = h'02

ack

address h'02

data

ack stop

ack from slave

ack from slave

LP3944

SNVS264 – MAY 2004

www.ti.com

an eighth bit which is a data direction bit (R/W). The LP3944 hardwires bits 7 to 4 and leaves bits 3 to 1

selectable, as shown in Figure 6. For the eighth bit, a “0” indicates a WRITE and a “1” indicates a READ. The

LP3944 supports only a WRITE during chip addressing. 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 6. Chip Address Byte

w = write (SDA = “0”)

r = read (SDA = “1”)

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

rs = repeated start

xx = 60 to 67

Figure 7. LP3944 Register Write

However, if a READ function is to be accomplished, a WRITE function must precede the READ function, as

shown in Figure 8.

w = write (SDA = “0”)

r = read (SDA = “1”)

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

rs = repeated start

xx = 60 to 67

Figure 8. LP3944 Register Read

Auto Increment

Auto increment is a special feature supported by the LP3944 to eliminate repeated chip and register addressing

when data are to be written to or read from registers in sequential order. The auto increment bit is inside the

register address byte, as shown in Figure 9. Auto increment is enabled when this bit is programmed to “1” and

disabled when it is programmed to “0”.

8

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