Datasheet

PIC16F627A/628A/648A

13.7 Using the Data EEPROM

The data EEPROM is a high endurance, byte

addressable array that has been optimized for the storage

of frequently changing information (e.g., program

variables or other data that are updated often). When

variables in one section change frequently, while

variables in another section do not change, it is possible

to exceed the total number of write cycles to the EEPROM

(specification D124) without exceeding the total number

of write cycles to a single byte (specifications D120 and

D120A). If this is the case, then an array refresh must be

performed. For this reason, variables that change

infrequently (such as constants, IDs, calibration, 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

Note: If data EEPROM is only used to store

constants and/or data that changes rarely,

an array refresh is likely not required. See

specification D124.

BANKSEL 0X80 ;select Bank1

CLRF EEADR ;start at address 0

BCF INTCON, GIE ;disable interrupts

BTFSC INTCON, GIE ;see AN576

GOTO $ - 2

BSF EECON1, WREN ;enable EE writes

Loop

BSF EECON1, RD ;retrieve data into EEDATA

MOVLW 0x55 ;first step of ...

MOVWF EECON2 ;... required sequence

MOVLW 0xAA ;second step of ...

MOVWF EECON2 ;... required sequence

BSF EECON1, WR ;start write sequence

BTFSC EECON1, WR ;wait for write complete

GOTO $ - 1

#IFDEF __16F648A ;256 bytes in 16F648A

INCFSZ EEADR, f ;test for end of memory

#ELSE ;128 bytes in 16F627A/628A

INCF EEADR, f ;next address

BTFSS EEADR, 7 ;test for end of memory

#ENDIF ;end of conditional assembly

GOTO Loop ;repeat for all locations

BCF EECON1, WREN ;disable EE writes

BSF INTCON, GIE ;enable interrupts (optional)