PIC16F628A-ISLASHML datasheet(94/168 Pages) MICROCHIP

94 / 168 page

PIC16F627A/628A/648A

DS40044A-page 92

Preliminary

 2002 Microchip Technology Inc.

13.7

Using the Data EEPROM

The data EEPROM is a high endurance, byte address-

able array that has been optimized for the storage of

frequently changing information (e.g., program vari-

ables or other data that are updated often). Frequently

changing values will typically be updated more often

than specification D124. If this is not the case, an array

refresh must be performed. For this reason, variables

that change infrequently (such as constants, IDs, cali-

bration, etc.) should be stored in FLASH program

memory.

A simple data EEPROM refresh routine is shown in

Example 13-4.

EXAMPLE 13-4:

DATA EEPROM REFRESH ROUTINE

13.8

DATA EEPROM OPERATION

DURING CODE PROTECT

When the device is code protected, the CPU is able to

read and write data to the Data EEPROM.

TABLE 13-1:

REGISTERS/BITS ASSOCIATED WITH DATA EEPROM

Note:

If data EEPROM is only used to store con-

stants and/or data that changes rarely, an

array refresh is likely not required. See

specification D124.

clrf

EEADR

; Start at address 0

bcf

EECON1,CFGS

; Set for memory

bcf

EECON1,EEPGD

; Set for Data EEPROM

bcf

INTCON,GIE

; Disable interrupts

bsf

EECON1,WREN

; Enable writes

Loop

; Loop to refresh array

bsf

EECON1,RD

; Read current address

movlw

55h

;

movwf

EECON2

; Write 55h

movlw

AAh

;

movwf

EECON2

; Write AAh

bsf

EECON1,WR

; Set WR bit to begin write

btfsc

EECON1,WR

; Wait for write to complete

bra

$-2

incfsz

EEADR,F

; Increment address

bra

Loop

; Not zero, do it again

bcf

EECON1,WREN

; Disable writes

bsf

INTCON,GIE

; Enable interrupts

Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on

Power-on

Reset

Value on all

other

RESETS

9Ah

EEDATA

EEPROM data register

xxxx xxxx

uuuu uuuu

9Bh

EEADR

EEPROM address register

xxxx xxxx

uuuu uuuu

9Ch

EECON1

—

WRERR

WREN

---- x000

---- q000

9Dh

EECON2(1)

EEPROM control register 2

---- ----

Legend:

x = unknown, u = unchanged, - = unimplemented read as '0', q = value depends upon condition.

Shaded cells are not used by data EEPROM.

Note

1: EECON2 is not a physical register

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