PIC12CE673-04SLASHP datasheet(30/116 Pages) MICROCHIP

30 / 116 page

PIC12CE67X

DS40181B-page 30

Preliminary

6.5

READ OPERATIONS

Read operations are initiated in the same way as write

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

EEPROM address is set to one. There are three basic

types of read operations: current address read, random

read, and sequential read.

6.5.1

CURRENT ADDRESS READ

It contains an address counter that maintains the

address of the last word accessed, internally incre-

mented by one. Therefore, if the previous read access

was to address n, the next current address read opera-

tion would access data from address n + 1. Upon

receipt of the EEPROM address with the R/W bit set to

one, the EEPROM issues an acknowledge and trans-

mits the eight bit data word. The processor will not

acknowledge the transfer but does generate a stop

condition and the EEPROM discontinues transmission

(Figure 6-6).

6.5.2

RANDOM READ

Random read operations allow the processor 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

EEPROM as part of a write operation. After the word

address is sent, the processor generates a start condi-

tion following the acknowledge. This terminates the

write operation, but not before the internal address

pointer is set. Then the processor issues the control

byte again but with the R/W bit set to a one. It will then

issue an acknowledge and transmits the eight bit data

word. The processor will not acknowledge the transfer

but does generate a stop condition and the EEPROM

discontinues transmission (Figure 6-7). After this com-

mand, the internal address counter will point to the

address location following the one that was just read.

6.5.3

SEQUENTIAL READ

Sequential reads are initiated in the same way as a ran-

dom read except that after the device transmits the ﬁrst

data byte, the processor issues an acknowledge as

opposed to a stop condition in a random read. This

directs the EEPROM to transmit the next sequentially

addressed 8-bit word (Figure 6-8).

To provide sequential reads, it contains an internal

address pointer which is incremented by one at the

completion of each read operation. This address

pointer allows the entire memory contents to be serially

read during one operation.

FIGURE 6-6:

CURRENT ADDRESS READ

FIGURE 6-7:

RANDOM READ

FIGURE 6-8:

SEQUENTIAL READ

BUS ACTIVITY

PROCESSOR

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

DATA

0 X X X 1

X = Don’t Care Bit

BUS ACTIVITY

PROCESSOR

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

WORD

ADDRESS (n)

CONTROL

BYTE

DATA (n)

X X X X

S 1

0 X X X 0

S 1

0 X X X 1

X = Don’t Care Bit

BUS ACTIVITY

PROCESSOR

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

DATA n

DATA n + 1

DATA n + 2

DATA n + X

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