Datasheet

Table Of Contents
PIC18F1220/1320
DS39605F-page 70 © 2007 Microchip Technology Inc.
7.7 Operation During Code-Protect
Data EEPROM memory has its own code-protect bits in
configuration words. External read and write
operations are disabled if either of these mechanisms
are 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 19.0
“Special Features of the CPU” for additional
information.
7.8 Using the Data EEPROM
The data EEPROM is a high endurance, byte address-
able array that has been optimized for the storage of fre-
quently changing information (e.g., program variables or
other data that are updated often). Frequently changing
values will typically be updated more often than specifi-
cation D124. If this is not the case, 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 7-3.
EXAMPLE 7-3: DATA EEPROM REFRESH ROUTINE
TABLE 7-1: REGISTERS ASSOCIATED WITH DATA EEPROM MEMORY
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.
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
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on:
POR, BOR
Value on
all other
Resets
INTCON GIE/GIEH PEIE/GIEL
TMR0IE INTE RBIE TMR0IF INTF RBIF 0000 000x 0000 000u
EEADR EEPROM Address Register 0000 0000 0000 0000
EEDATA EEPROM Data Register 0000 0000 0000 0000
EECON2 EEPROM Control Register 2 (not a physical register)
EECON1 EEPGD CFGS
FREE WRERR WREN WR RD xx-0 x000 uu-0 u000
IPR2 OSCFIP
—EEIP LVDIP TMR3IP 1--1 -11- 1--1 -11-
PIR2 OSCFIF
—EEIF LVDIF TMR3IF 0--0 -00- 0--0 -00-
PIE2 OSCFIE
—EEIE LVDIE TMR3IE 0--0 -00- 0--0 -00-
Legend: x = unknown, u = unchanged, – = unimplemented, read as ‘0’. Shaded cells are not used during Flash/EEPROM access.