11

FN8249.0

April 28, 2005

Device Addressing

Following a start condition, the master must output a Slave

Address Byte. The rst four bits of the Slave Address Byte

specify access to the EEPROM array or to the CCR. Slave

bits ‘1010’ access the EEPROM array. Slave bits ‘1101’

access the CCR.

Bit 3 through Bit 1 of the slave byte specify the device select

bits.These are set to ‘111’.

The last bit of the Slave Address Byte denes the oper-ation

to be performed. When this R/W bit is a one, then a read

operation is selected. A zero selects a write operation. Refer

to Figure 12.

After loading the entire Slave Address Byte from the SDA

bus, the device compares the device identier and device

select bits with ‘1010111’ or ‘1101111’. Upon a correct

compare, the device outputs an acknowledge on the SDA

line.

Following the Slave Byte is a two byte word address. The

word address is either supplied by the master device or

obtained from an internal counter. On power up the internal

address counter is set to address 0h, so a current address

read of the EEPROM array starts at address 0. When

required, as part of a random read, the master device must

supply the 2 Word Address Bytes.

In a random read operation, the slave byte in the “dummy

write” portion must match the slave byte in the “read”

section. That is if the random read is from the array the slave

byte must be ‘1010111x’ in both instances. Similarly, for a

random read of the Clock/ Control Registers, the slave byte

must be ‘1101111x’ in both places.

Data

(2)

S

t

o

p

Slave

Address

Data

(n)

A

C

K

A

C

K

SDA Bus

Signals from

the Slave

Signals from

the Master

1

Data

(n-1)

A

C

K

A

C

K

(n is any integer greater than 1)

Data

(1)

FIGURE 12. SEQUENTIAL READ SEQUENCE

Slave Address Byte

Byte 0

D7

D6

D5

D2

D4

D3

D1

D0

A0

A7

A2

A4

A3

A1

Data Byte

Byte 3

A6

A5

0

0

0

A10

A9

A8

0

1

1

0

1

1

0

1

0

1

1

R/W

1

Device Identifier

Array

CCR

0

High Order Word Address

Byte 1

Low Order Word Address

Byte 2

FIGURE 13. SLAVE ADDRESS, WORD ADDRESS, AND DATA BYTES (64-BYTE PAGES)

X1243