Bit Read: At the end a write operation, the master must

release the SDA bus line for the proper amount of setup

time (see Figure 3) before the next rising edge of SCL

during a bit read. The device shifts out each bit of data

on SDA at the falling edge of the previous SCL pulse

and the data bit is valid at the rising edge of the current

SCL pulse. Remember that the master generates all

SCL clock pulses including when it is reading bits from

the slave.

Acknowledgement (ACK): An Acknowledgement

(ACK) is always the 9th 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 transmitting a zero during the 9th bit. For tim-

ing, see Figure 3. An ACK is the acknowledgement that

the device is properly receiving data.

Byte Write: A byte write consists of 8 bits of informa-

tion transferred from the master to the slave (most sig-

nificant bit first) plus a 1-bit acknowledgement from the

slave to the master. The 8 bits transmitted by the mas-

ter 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 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 ACK the last byte read to termi-

nated communication so the slave returns control of

SDA to the master.

2-wire bus responds to a slave addressing byte sent

immediately following a START condition. The slave

address byte contains the slave address and the R/W

bit. The slave address (see Figure 4) is the most signifi-

cant 7 bits and the R/W bit is the least significant bit.

The DS4302’s slave address is 0101100X (binary),

where X is the R/W bit. If the R/W bit is zero

(01011000), the master will write data to the slave. If the

R/W is a one (01011001), the master will read data from

the slave.

Memory Address: During a 2-wire write operation, the

master must transmit a memory address to identify the

memory location where the slave is to store the data.

The memory address is the second byte transmitted

during a write or read operation following the slave

address byte (R/W=0). For a write operation, the mem-

ory address is 10101010 (AAh) and for a read opera-

tion, the memory address is 00000000 (00h).

2-Wire, 5-Bit DAC with Three Digital Outputs

_____________________________________________________________________

7

7-BIT SLAVE ADDRESS

MOST

SIGNIFICANT

BIT

DETERMINES

READ OR WRITE

R/W

0

0

1

1

0

1

0

Figure 4. Slave Address and the R/W Bit

Figure 3. 2-Wire Timing Diagram

SDA

SCL

STOP

START

REPEATED

START