24VL024HTSLASHMS datasheet(11/28 Pages) MICROCHIP

11 / 28 page

DS22109A-page 11

24VL024H

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 24VL024H contains an address counter that main-

tains 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 24VL024H 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

24VL024H 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

24VL024H 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 24VL024H will then issue an acknowledge and

transmits the eight-bit data word. The master will not

acknowledge the transfer, but does generate a Stop

condition and the 24VL024H 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 24VL024H transmits

the first data byte, the master issues an acknowledge

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

directs the 24VL024H to transmit the next sequentially

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

To provide sequential reads, the 24VL024H 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 FFh to

address 00h.

FIGURE 8-1:

CURRENT ADDRESS READ

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Data

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