24VL024SLASHMS datasheet(11/30 Pages) MICROCHIP

11 / 30 page

DS22130A-page 11

24VL024/24VL025

8.0

READ OPERATIONS

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.

8.1

Current Address Read

The

24VL024/24VL025

contains

address

counter that maintains the address of the last word

accessed, internally incremented by one. Therefore, if

the previous read access was to address n, the next

current address read operation would access data from

address n + 1. Upon receipt of the slave address with

the R/W bit set to ‘1’, the 24VL024/24VL025 issues an

acknowledge and transmits the 8-bit data word. The

master will not acknowledge the transfer, but does

generate a Stop condition and the 24VL024/24VL025

discontinues transmission (Figure 8-1).

8.2

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 done by sending the word address to the

24VL024/24VL025 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

24VL024/24VL025

will

then

issue

acknowledge and transmits the eight-bit data word.

The master will not acknowledge the transfer, but does

generate a Stop condition and the 24VL024/24VL025

discontinues

transmission (Figure 8-2). After this

command, the internal address counter 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 a

random read except that after the 24VL024/24VL025

transmits the first data byte, the master issues an

acknowledge as opposed to a Stop condition in a

random read. This directs the 24VL024 to transmit the

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

To provide sequential reads, the 24VL024/24VL025

contains

internal

Address

Pointer

which

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 FFh to address

00h.

FIGURE 8-1:

CURRENT ADDRESS READ

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Data

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