HT24LC64 datasheet(4/10 Pages) HOLTEK

4 / 10 page

HT24LC64

Rev. 1.00

January 5, 2005

· Write protect

The HT24LC64 has a write-protect function and pro-

gramming will then be inhibited when the WP pin is

connected to VCC. Under this mode, the HT24LC64 is

used as a serial ROM.

· Read operations

The HT24LC64 supports three read operations,

namely, current address read, random address read

and sequential read. During read operation execution,

the read/write select bit should be set to

²1².

· Current address read

The internal data word address counter maintains the

last address accessed during the last read or write op-

eration, incremented by one. This address remains

valid between operations as long as the chip power is

maintained. The address will roll over during read

from the last byte of the last memory page to the first

byte of the first page. The address will roll over during

write from the last byte of the current page to the first

byte of the same page. Once the device address with

the read/write select bit set to one is clocked in and ac-

knowledged by the EEPROM, the current address

data word is serially clocked out. The microcontroller

does not respond with an input zero but generates a

following stop condition (refer to Current read timing).

· Random read

A random read requires a dummy byte write sequence

to load in the data word address which is then clocked

in and acknowledged by the EEPROM. The

microcontroller must then generate another start con-

dition. The microcontroller now initiates a current ad-

dress read by sending a device address with the

read/write select bit high. The EEPROM acknowl-

edges the device address and serially clocks out the

data word. The microcontroller should respond with a

²no ACK² signal (high) followed by a stop condition

(refer to Random read timing).

· Sequential read

Sequential reads are initiated by either a current ad-

dress read or a random address read. After the

microcontroller receives a data word, it responds with

an acknowledgment. As long as the EEPROM re-

ceives an acknowledgment, it will continue to incre-

ment the data word address and serially clock out

sequential data words. When the memory address

limit is reached, the data word address will roll over

and the sequential read continues. The sequential

read operation is terminated when the microcontroller

does not respond with a zero but generates a following

stop condition.

D e v i c e A d d r e s s

1 s t , 2 n d W o r d

A d d r e s s ( n )

S D A L i n e

A 2 A 1 A 0

D e v i c e A d d r e s s

D a t a ( n )

D u m m y W r i t e

N o t e : * = D o n ' t c a r e b i t s

Random Read Timing

A 2 A 1 A 0

D e v i c e a d d r e s s

D a t a

S D A L i n e

Current Address Read Timing

S D A L i n e

D a t a ( n + x )

D a t a ( n + 2 )

D a t a ( n + 1 )

D a t a ( n )

D e v i c e

A d d r e s s

Sequential Read Timing

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