Datasheet

PIC18(L)F1XK22
DS41365E-page 60  2009-2011 Microchip Technology Inc.
5.6 Operation During Code-Protect
Data EEPROM memory has its own code-protect bits in
Configuration Words. External read and write
operations are disabled if code protection is enabled.
The microcontroller itself can both read and write to the
internal data EEPROM, regardless of the state of the
code-protect Configuration bit. Refer to Section 22.0
“Special Features of the CPU” for additional
information.
5.7 Protection Against Spurious Write
There are conditions when the user may not want to
write to the data EEPROM memory. To protect against
spurious EEPROM writes, various mechanisms have
been implemented. On power-up, the WREN bit is
cleared. In addition, writes to the EEPROM are blocked
during the Power-up Timer period (T
PWRT,
parameter 33).
The write initiate sequence and the WREN bit together
help prevent an accidental write during brown-out,
power glitch or software malfunction.
5.8 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 without exceeding the total number of write
cycles to a single byte. 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.
EXAMPLE 5-3: DATA EEPROM REFRESH ROUTINE
TABLE 5-1: REGISTERS ASSOCIATED WITH DATA EEPROM MEMORY
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Reset
Values
on page
EEADR EEADR7 EEADR6 EEADR5 EEADR4 EEADR3 EEADR2 EEADR1 EEADR0 255
EECON1 EEPGD CFGS — FREE WRERR WREN WR RD 255
EECON2 EEPROM Control Register 2 (not a physical register) 255
EEDATA EEPROM Data Register 255
INTCON GIE/GIEH PEIE/GIEL TMR0IE INT0IE RABIE TMR0IF INT0IF RABIF 253
IPR2
OSCFIP C1IP C2IP EEIP BCLIP — TMR3IP — 256
PIE2
OSCFIE C1IE C2IE EEIE BCLIE — TMR3IE — 256
PIR2 OSCFIF C1IF C2IF EEIF BCLIF — TMR3IF — 256
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used during Flash/EEPROM access.
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 0AAh ;
MOVWF EECON2 ; Write 0AAh
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