PIC12C67X datasheet(37/129 Pages) MICROCHIP

37 / 129 page

DS30561B-page 37

PIC12C67X

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

The EEPROM 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 EEPROM address with the R/W bit set to

one, the EEPROM issues an acknowledge and trans-

mits the 8-bit data word. The processor will not

acknowledge the transfer, but does generate a stop

condition and the EEPROM discontinues transmission

(Figure 6-8).

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. The

EEPROM will then issue an acknowledge and trans-

mits the 8-bit data word. The processor will not

acknowledge the transfer, but does generate a stop

condition and the EEPROM discontinues transmission

(Figure 6-9). After this command, 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 6-10).

To provide sequential reads, the EEPROM 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 6-8:

CURRENT ADDRESS READ

FIGURE 6-9:

RANDOM READ

FIGURE 6-10: SEQUENTIAL READ

SDA LINE

CONTROL

BYTE

DATA

00 X X X 1

X = Don’t Care Bit

ACTIVITY

SDA LINE

CONTROL

BYTE

WORD

ADDRESS (n)

CONTROL

BYTE

DATA (n)

XX X X

00 X X X 0

00 X X X 1

X = Don’t Care Bit

ACTIVITY

SDA LINE

CONTROL

BYTE

DATA n

DATA n + 1

DATA n + 2

DATA n + X

ACTIVITY

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