T48C893 datasheet(75/82 Pages) ATMEL

75 / 82 page

T48C893

Rev. A4, 22-Jan-02

75 (82)

Read Operations

The EEPROM allows byte-, word- and current address

read operations. The read operations are initiated in the

same way as write operations. Every read access is initi-

ated by sending the START condition followed by the

control byte which contains the address and the read

mode. After the device receives a read command it re-

turns an acknowledge, loads the addressed word into the

read\write buffer and sends the selected data byte to the

master. The master has to acknowledge the received byte

if it wants to proceed the read operation. If two bytes are

read out from the buffer the device increments respec-

tively decrements the word address automatically and

loads the buffer with the next word. The read mode bits

determines if the low or high byte is read first from the

buffer and if the word address is incremented or decre-

mented for the next read access. If the memory address

limit is reached, the data word address will ”roll over” and

the sequential read will continue. The master can termi-

nate the read operation after every byte by not responding

with an acknowledge (N) and by issuing a stop condition.

Read One Data Byte

Start

Control byte

Data byte 1

Stop

Read Two Data Bytes

Start

Control byte

Data byte 1

Data byte 2

Stop

Read n Data Bytes

Start

Control byte

Data byte 1

Data byte 2

– – – –

Data byte n

Stop

Read Control Bytes

MSB

LSB

Read low byte first, address increment

R/NW

Row address

Byte order

LB(R)

HB(R)

LB(R+1)

HB(R+1)

– – –

LB(R+n)

HB(R+n)

MSB

LSB

Read high byte first, addr. decrement

R/NW

Row address

Byte order

HB(R)

LB(R)

HB(R–1)

LB(R–1)

– – –

HB(R–n)

LB(R–n)

A –> acknowledge, N –> no acknowledge; HB: high byte; LB: low byte, R: row address

Initialization the Serial Interface to the EEPROM

To prevent unexpected behaviour of the EEPROM and its interface it is good practice to use an initialization sequence

after any reset of the circuit. This is performed by writing:

Start

“FFh”

Stop

to the serial interface. If the EEPROM acknowledges this sequence it is in a defined state. Maybe it is necessary to

perform this sequence twice.

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