24LC08B-ESLASHMSG datasheet(9/26 Pages) MICROCHIP

9 / 26 page

DS21710H-page 9

24AA08/24LC08B

7.0

READ OPERATION

Read operations are initiated in the same way as write

operations, with the exception that the R/W bit of the

slave address is set to ‘

1’. There are three basic types

of read operations: current address read, random read

and sequential read.

7.1

Current Address Read

The 24XX08 contains an address counter that main-

tains the address of the last word accessed, internally

incremented by ‘

1’. Therefore, if the previous access

(either a read or write operation) was to address

n, the

next current address read operation would access data

from address

n + 1. Upon receipt of the slave address

with R/W bit set to ‘

1’, the 24XX08 issues an acknowl-

edge and transmits the 8-bit data word. The master will

not acknowledge the transfer, but does generate a Stop

condition and the 24XX08 discontinues transmission

(Figure 7-1).

7.2

Random Read

Random read operations allow the master to access

any memory location in a random manner. To perform

this type of read operation, the word address must first

be set. This is accomplished by sending the word

address to the 24XX08 as part of a write operation.

Once the word address is sent, the master generates a

Start condition following the acknowledge. This

terminates the write operation, but not before the

internal Address Pointer is set. The master then issues

the control byte again, but with the R/W bit set to a ‘

1’.

The 24XX08 will then issue an acknowledge and trans-

mit the 8-bit data word. The master will not acknowl-

edge the transfer, but does generate a Stop condition

and the 24XX08 will discontinue transmission

(Figure 7-2).

7.3

Sequential Read

Sequential reads are initiated in the same way as a

random read, except that once the 24XX08 transmits

the first data byte, the master issues an acknowledge

as opposed to a Stop condition in a random read. This

directs the 24XX08 to transmit the next sequentially-

addressed 8-bit word (Figure 7-3).

To provide sequential reads, the 24XX08 contains an

internal Address Pointer that is incremented by one

upon completion of each operation. This Address

Pointer allows the entire memory contents to be serially

read during one operation.

7.4

Noise Protection

The 24XX08 employs a VCC threshold detector circuit

which disables the internal erase/write logic if the VCC

is below 1.5V at nominal conditions.

The SCL and SDA inputs have Schmitt Trigger and

filter circuits which suppress noise spikes to assure

proper device operation, even on a noisy bus.

FIGURE 7-1:

CURRENT ADDRESS READ

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Data (n)

x = “don’t care”

1 01 0 x B1 B0 1

Block

Select

Bits

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