PIC18F-LF1XK50 Datasheet, PDF (64/420 Pages) Microchip Technology – 20-Pin USB Flash Microcontrollers

PIC18F/LF1XK50
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 24.0
“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 (TPWRT,
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:
Loop
CLRF
BCF
BCF
BCF
BSF
BSF
MOVLW
MOVWF
MOVLW
MOVWF
BSF
BTFSC
BRA
INCFSZ
BRA
BCF
BSF
DATA EEPROM REFRESH ROUTINE
EEADR
EECON1, CFGS
EECON1, EEPGD
INTCON, GIE
EECON1, WREN
EECON1, RD
55h
EECON2
0AAh
EECON2
EECON1, WR
EECON1, WR
$-2
EEADR, F
LOOP
; Start at address 0
; Set for memory
; Set for Data EEPROM
; Disable interrupts
; Enable writes
; Loop to refresh array
; Read current address
;
; Write 55h
;
; Write 0AAh
; Set WR bit to begin write
; Wait for write to complete
; Increment address
; Not zero, do it again
EECON1, WREN
INTCON, GIE
; Disable writes
; Enable interrupts
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
INTCON GIE/GIEH PEIE/GIEL TMR0IE INT0IE RABIE TMR0IF INT0IF RABIF
285
EEADR
EEADR7 EEADR6 EEADR5 EEADR4 EEADR3 EEADR2 EEADR1 EEADR0 287
EEDATA EEPROM Data Register
287
EECON2 EEPROM Control Register 2 (not a physical register)
287
EECON1
EEPGD
CFGS
—
FREE WRERR WREN WR
RD
287
IPR2
OSCFIP
C1IP
C2IP
EEIP BCLIP USBIP TMR3IP
—
288
PIR2
OSCFIF
C1IF
C2IF
EEIF BCLIF USBIF TMR3IF
—
288
PIE2
OSCFIE
C1IE
C2IE
EEIE BCLIE USBIE TMR3IE
—
288
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used during Flash/EEPROM access.
DS41350E-page 64
Preliminary
 2010 Microchip Technology Inc.