24LC64XT-ESLASHCS16K datasheet(13/51 Pages) MICROCHIP

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DS20001189U-page 13

24AA64/24FC64/24LC64

8.0

READ OPERATION

Read operations are initiated in the same way as write

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

control byte is set to one. There are three basic types

of read operations: current address read, random read

and sequential read.

8.1

Current Address Read

The 24XX64 contains an Address Pointer that main-

tains the address of the last word accessed, internally

incremented by one. Therefore, if the previous read

access was to address ‘n’ (n is any legal address), the

next current address read operation would access data

from address n + 1.

Upon receipt of the control byte with R/W bit set to one,

the 24XX64 issues an Acknowledge and transmits the

8-bit data word. The host will not acknowledge the

transfer, but does generate a Stop condition and the

24XX64 discontinues transmission (Figure 8-1).

8.2

Random Read

Random read operations allow the host 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 24XX64 as part of a write

operation (R/W bit set to ‘0’). Once the word address

is sent, the host generates a Start condition following

the Acknowledge.

This terminates the write operation, but not before

the internal Address Pointer is set. The host then

issues the control byte again, but with the R/W bit set

to a ‘1’. The 24XX64 will then issue an Acknowledge

and transmit the 8-bit data word. The host will not

acknowledge the transfer, but does generate a Stop

condition, which causes the 24XX64 to discontinue

transmission (Figure 8-2). After a random Read

command, the internal Address Pointer will point to

the address location following the one that was just

read.

8.3

Sequential Read

Sequential reads are initiated in the same way as

random reads, except that once the 24XX64 transmits

the first data byte, the host issues an Acknowledge as

opposed to the Stop condition used in a random read.

This Acknowledge directs the 24XX64 to transmit the

next sequentially-addressed 8-bit word (Figure 8-3).

Following the final byte being transmitted to the host,

the host will NOT generate an Acknowledge, but will

generate a Stop condition. To provide sequential reads,

the 24XX64 contains an internal Address Pointer which

is incremented by one at the completion of each

operation. This Address Pointer allows the entire

memory contents to be serially read during one

operation.

The

internal Address

Pointer

will

automatically roll over from address 1FFF to address

0000 if the host acknowledges the byte received from

the array address 1FFF.

FIGURE 8-1:

CURRENT ADDRESS READ

Bus Activity

Host

SDA Line

Bus Activity

Control

Byte

Data Byte

10 1

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