24C01C datasheet(11/30 Pages) MICROCHIP

11 / 30 page

DS21201J-page 11

24C01C

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

slave address 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 24C01C 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 one,

the 24C01C issues an acknowledge and transmits the

eight-bit data word. The master will not acknowledge

the transfer, but does generate a Stop condition and the

24C01C discontinues transmission (Figure 8-1).

FIGURE 8-1:

CURRENT ADDRESS

READ

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, first the word address must

be set. This is done by sending the word address to the

24C01C as part of a write operation.

After 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. Then the master issues

the control byte again but with the R/W bit set to a one.

The 24C01C will then issue an acknowledge and trans-

mits the eight bit data word. The master will not

acknowledge the transfer, but does generate a Stop

condition and the 24C01C 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 24C01C transmits

the first data byte, the master issues an acknowledge

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

directs the 24C01C to transmit the next sequentially

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

To provide sequential reads the 24C01C 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 7F to

address 00.

FIGURE 8-2:

RANDOM READ

FIGURE 8-3:

SEQUENTIAL READ

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Data

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Word

Address (n)

Control

Byte

Data (n)

Bus Activity

Master

SDA Line

Bus Activity

Control

Byte

Data n

Data n + 1

Data n + 2

Data n + X

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