Acknowledgement (ACK and NACK): An Acknowledge-

ment (ACK) or Not Acknowledge (NACK) is always the

ninth bit transmitted during a byte transfer. The device

receiving data (the master during a read or the slave

during a write operation) performs an ACK by transmit-

ting a zero during the ninth bit. A device performs a

NACK by transmitting a one during the ninth bit. Timing

for the ACK and NACK is identical to all other bit writes

(Figure 4). An ACK is the acknowledgment that the

device is properly receiving data. A NACK is used to

terminate a read sequence or as an indication that the

device is not receiving data.

Byte Write: A byte write consists of 8 bits of information

transferred from the master to the slave (most significant

bit first) plus a 1-bit acknowledgement from the slave to

the master. The 8 bits transmitted by the master are

done according to the bit-write definition, and the

acknowledgement is read using the bit-read definition.

Byte Read: A byte read is an 8-bit information transfer

from the slave to the master plus a 1-bit ACK or NACK

from the master to the slave. The 8 bits of information

that are transferred (most significant bit first) from the

slave to the master are read by the master using the bit

read definition above, and the master transmits an ACK

using the bit write definition to receive additional data

bytes. The master must NACK the last byte read to ter-

minated communication so the slave will return control

of SDA to the master.

responds to a slave address byte sent immediately follow-

ing a START condition. The slave address byte contains

the slave address in the most significant 7 bits and the

slave address is determined by the state of the A0 and A1

address pins. Table 1 describes the addresses corre-

sponding to the state of A0 and A1.

When the R/W bit is 0 (such as in A0h), the master is

indicating it will write data to the slave. If R/W = 1 (A1h

in this case), the master is indicating it wants to read

from the slave. If an incorrect slave address is written,

the DS4402/DS4404 assume the master is communi-

nication until the next START condition is sent.

master must transmit a memory address to identify the

memory location where the slave is to store the data.

The memory address is always the second byte trans-

mitted during a write operation following the slave

address byte.

Writing to a Slave: The master must generate a START

condition, write the slave address byte (R/W = 0), write

the memory address, write the byte of data, and gener-

ate a STOP condition. Remember that the master must

read the slave’s acknowledgement during all byte-write

operations.

Reading from a Slave: To read from the slave, the

master generates a START condition, writes the slave

address byte with R/W = 1, reads the data byte with a

NACK to indicate the end of the transfer, and generates

a STOP condition.

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7

SDA

SCL

REPEATED

START

STOP

START