PIC18F2420-I/SOC01 Microchip, PIC18F2420-I/SOC01 Datasheet - Page 88
PIC18F2420-I/SOC01
Manufacturer Part Number
PIC18F2420-I/SOC01
Description
28 pin, 16 kb flash, 3804 ram, 25 i/o...
Manufacturer
Microchip
Datasheet
1.PIC18F2420-ISOC01.pdf
(412 pages)
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PIC18F2420/2520/4420/4520
7.6
Data EEPROM memory has its own code-protect bits in
Configuration
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 23.0
“Special Features of the CPU” for additional
information.
7.7
There are conditions when the user may not want to write
to the data EEPROM memory. To protect against spuri-
ous 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
The write initiate sequence and the WREN bit together
help prevent an accidental write during brown-out,
power glitch or software malfunction.
EXAMPLE 7-3:
DS39631E-page 86
Loop
Operation During Code-Protect
Protection Against Spurious Write
CLRF
BCF
BCF
BCF
BSF
BSF
MOVLW
MOVWF
MOVLW
MOVWF
BSF
BTFSC
BRA
INCFSZ EEADR, F
BRA
BCF
BSF
Words.
EEADR
EECON1, CFGS
EECON1, EEPGD
INTCON, GIE
EECON1, WREN
EECON1, RD
55h
EECON2
0AAh
EECON2
EECON1, WR
EECON1, WR
$-2
LOOP
EECON1, WREN
INTCON, GIE
DATA EEPROM REFRESH ROUTINE
PWRT
External
, parameter 33).
read
; 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
; Disable writes
; Enable interrupts
and
write
7.8
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). Frequently changing values will typically be
updated more often than specification 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.
Note:
Using the Data EEPROM
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.
© 2008 Microchip Technology Inc.
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