HT46R46E datasheet(19/73 Pages) HOLTEK

19 / 73 page

HT46R46E/C46E/R47E/C47E/R48AE/C48AE/R49E

Rev. 1.20

August 15, 2007

Read Operations

There are three kinds of read operation. These are cur-

rent address read, random read and sequential read.

· Current Address Read

Inside the EEPROM is an internal counter which will

point to the present EEPROM address. This internal

counter will increment by one each time a read or write

operation is executed. The value of the counter will be

stored as long as the EEPROM is powered up, only

when power is removed will the counter lose its value.

If it is required to read the data at the address that this

internal counter is pointing to, then it is not necessary

to send any address information to the EEPROM.

Therefore for a current address read operation to be

executed, after the device address and read/write bit

information has been sent, if the read/write bit is set

high, then after the EEPROM sends its acknowledge

signal by pulling SDA low on the ninth clock pulse, it

will transmit its internal 8-bits of data at this address

on the following eight clock pulses. After the 8-bits of

data have been received, no acknowledge is sent but

a STOP condition should be transmitted by the receiv-

ing device to end the read execution.

· Random Read

A random read operation allows data at any address

within the EEPROM to be read out. For this to happen,

a start condition, device address and read/write bit

must first be transmitted. Then after the usual ac-

knowledge signal is received from the EEPROM, the

required EEPROM internal address information must

be transmitted. In this case, as an address is being

written to the EEPROM, the read/write bit should be

low. After the 8-bit address has been transmitted, in

an MSB first format, the EEPROM will respond with

another acknowledge signal. At this point, the internal

counter is now pointing to the requested address.

Now the data can be read out by sending another

start, device address and read/write bit information,

but this time with the read/write bit set high to indicate

a read operation. After the EEPROM acknowledges

this in the usual way, the 8-bits of data at the re-

quested address can be read out. As this read opera-

tion is the same as the current address read

operation, no acknowledge signal will be generated

but a stop condition must be sent to the EEPROM to

end the read execution.

· Sequential Read

A sequential read allows more than one byte of data to

be read out of the EEPROM sequentially. It utilises the

EEPROM internal counter, which points to the

EEPROM internal address, and which will increment

by one automatically after each byte of data has been

read out. A sequential read operation is started by first

executing a random read or current read to setup the

start address of the data to be read out. After the first

byte of data has been read out of the EEPROM using

the current read or random read, instead of sending a

STOP condition, an acknowledge is sent instead. This

is achieved by the receiving device pulling the SDA

line low on the clock pulse after the eighth data bit.

When the EEPROM receives this acknowledge it will

automatically increment its internal counter allowing

the next byte of data to be read out. Note that when

the address counter reaches its maximum value its

next value will automatically roll over to zero.

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

D a t a f r o m E E P R O M

S t o p

S t a r t

S D A

R / W h i g h

- - R e a d

A c k n o w l e d g e

f r o m E E P R O M

S D A p u l l e d l o w

N o a c k n o w l e d g e

S D A f l o a t s h i g h

Current Address Read

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

W o r d a d d r e s s

S t o p

S D A

D a t a

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

S t a r t

0 0 0 0

R / W l o w

- - W r i t e

A c k n o w l e d g e

f r o m E E P R O M

S D A p u l l e d l o w

N o a c k n o w l e d g e

S D A f l o a t s h i g h

S t a r t

0 0 0 0 R

R / W h i g h

- - R e a d

Random Read

C u r r e n t a d d r e s s r e a d o r

r a n d o m r e a d o p e r a t i o n

D a t a n

S D A

D a t a n + 1

D a t a n + x

S t o p

N o a c k n o w l e d g e

S D A f l o a t s h i g h

R / W h i g h

- - R e a d

0 0 R

A c k n o w l e d g e f r o m r e c e i v i n g d e v i c e

S D A p u l l e d l o w

Sequential Read

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