Datasheet

Table Of Contents
© 2009 Microchip Technology Inc. DS39689F-page 87
PIC18F2221/2321/4221/4321 FAMILY
EXAMPLE 7-3: WRITING TO FLASH PROGRAM MEMORY (CONTINUED)
7.5.2 WRITE VERIFY
Depending on the application, good programming
practice may dictate that the value written to the
memory should be verified against the original value.
This should be used in applications where excessive
writes can stress bits near the specification limit.
7.5.3 UNEXPECTED TERMINATION OF
WRITE OPERATION
If a write is terminated by an unplanned event, such as
loss of power or an unexpected Reset, the memory
location just programmed should be verified and repro-
grammed if needed. If the write operation is interrupted
by a MCLR
Reset or a WDT Time-out Reset during
normal operation, the user can check the WRERR bit
and rewrite the location(s) as needed.
7.5.4 PROTECTION AGAINST
SPURIOUS WRITES
To protect against spurious writes to Flash program
memory, the write initiate sequence must also be
followed. See Section 24.0 “Special Features of the
CPU” for more detail.
7.6 Flash Program Operation During
Code Protection
See Section 24.5 “Program Verification and Code
Protection” for details on code protection of Flash
program memory.
TABLE 7-2: REGISTERS ASSOCIATED WITH PROGRAM FLASH MEMORY
PROGRAM_MEMORY
BCF INTCON, GIE ; disable interrupts
MOVLW 55h ; required sequence
MOVWF EECON2 ; write 55h
MOVLW 0AAh
MOVWF EECON2 ; write AAh
BSF EECON1, WR ; start program (CPU stall)
NOP
BSF INTCON, GIE ; re-enable interrupts
DECFSZ COUNTER_HI ; loop until done
GOTO PROGRAM_LOOP
BCF EECON1, WREN ; disable write to memory
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Reset
Values on
page
TBLPTRU
bit 21 Program Memory Table Pointer Upper Byte (TBLPTR<20:16>) 55
TBPLTRH Program Memory Table Pointer High Byte (TBLPTR<15:8>) 55
TBLPTRL Program Memory Table Pointer Low Byte (TBLPTR<7:0>) 55
TABLAT Program Memory Table Latch 55
INTCON GIE/GIEH PEIE/GIEL
TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 55
EECON2 EEPROM Control Register 2 (not a physical register) 57
EECON1 EEPGD CFGS
FREE WRERR WREN WR RD 57
IPR2
OSCFIP CMIP EEIP BCLIP HLVDIP TMR3IP CCP2IP 58
PIR2
OSCFIF CMIF EEIF BCLIF HLVDIF TMR3IF CCP2IF 58
PIE2
OSCFIE CMIE EEIE BCLIE HLVDIE TMR3IE CCP2IE 58
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used during Flash/EEPROM access.