11

FN6177.0

July 28, 2006

condition, which is a LOW to HIGH transition of SDA while

SCL is HIGH (See Figure 16). A STOP condition at the end

of a read operation, or at the end of a write operation places

the device in its standby mode.

An ACK, Acknowledge, is a software convention used to

indicate a successful data transfer. The transmitting device,

either master or slave, releases the SDA bus after

transmitting eight bits. During the ninth clock cycle, the

receiver pulls the SDA line LOW to acknowledge the

reception of the eight bits of data (See Figure 17).

The ISL22346 responds with an ACK after recognition of a

START condition followed by a valid Identification Byte, and

once again after successful receipt of an Address Byte. The

ISL22346 also responds with an ACK after receiving a Data

Byte of a write operation. The master must respond with an

ACK after receiving a Data Byte of a read operation.

A valid Identification Byte contains 1010 as the four MSBs,

and the following three bits matching the logic values

present at pins A2, A1, and A0. The LSB is the Read/Write

bit. Its value is “1” for a Read operation, and “0” for a Write

operation (See Table 3).

TABLE 3. IDENTIFICATION BYTE FORMAT

1010

A2

A1

A0

R/W

(MSB)

(LSB)

Logic values at pins A2, A1, and A0 respectively

SDA

SCL

START

DATA

DATA

STOP

STABLE

CHANGE

DATA

STABLE

FIGURE 16. VALID DATA CHANGES, START, AND STOP CONDITIONS

SDA OUTPUT FROM

TRANSMITTER

SDA OUTPUT FROM

RECEIVER

8

1

9

START

ACK

SCL FROM

MASTER

HIGH IMPEDANCE

HIGH IMPEDANCE

FIGURE 17. ACKNOWLEDGE RESPONSE FROM RECEIVER

S

T

A

R

T

S

T

O

P

IDENTIFICATION

BYTE

ADDRESS

BYTE

DATA

BYTE

A

C

K

SIGNALS FROM

THE MASTER

SIGNALS FROM

THE SLAVE

A

C

K

1

0

1

00

A

C

K

WRITE

SIGNAL AT SDA

00 0 0

A0

A1

A2

0

FIGURE 18. BYTE WRITE SEQUENCE

ISL22346