PIC18F452I/L Microchip Technology, PIC18F452I/L Datasheet - Page 70

• Manufacturer Part Number: PIC18F452I/L
• Description: IC, 8BIT MCU, PIC18F, 40MHZ, LCC-44
• Manufacturer: Microchip Technology

Specifications of PIC18F452I/L

• Controller Family/series: PIC18
• No. Of I/o's: 34
• Eeprom Memory Size: 256Byte
• Ram Memory Size: 1.5KB
• Cpu Speed: 40MHz
• No. Of Timers: 4
• Core Size: 8 Bit
• Program Memory Size: 16 KWords
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PIC18FXX2
6.5
Depending on the application, good programming
practice may dictate that the value written to the mem-
ory should be verified against the original value. This
should be used in applications where excessive writes
can stress bits near the specification limit.
6.6
There are conditions when the device may not want to
write to the data EEPROM memory. To protect against
spurious EEPROM writes, various mechanisms have
been built-in. On power-up, the WREN bit is cleared.
Also, the Power-up Timer (72 ms duration) prevents
EEPROM write.
The write initiate sequence and the WREN bit together
help prevent an accidental write during brown-out,
power glitch, or software malfunction.
EXAMPLE 6-3:
DS39564C-page 68
Loop
Write Verify
Protection Against Spurious Write
clrf
bcf
bcf
bcf
bsf
bsf
movlw
movwf
movlw
movwf
bsf
btfsc
bra
incfsz EEADR,F
bra
bcf
bsf
EEADR
EECON1,CFGS
EECON1,EEPGD
INTCON,GIE
EECON1,WREN
EECON1,RD
55h
EECON2
AAh
EECON2
EECON1,WR
EECON1,WR
$-2
Loop
EECON1,WREN
INTCON,GIE
DATA EEPROM REFRESH ROUTINE
; 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 AAh
; Set WR bit to begin write
; Wait for write to complete
; Increment address
; Not zero, do it again
; Disable writes
; Enable interrupts
6.7
Data EEPROM memory has its own code protect
mechanism. 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 “Special Features
of the CPU” (Section 19.0) for additional information.
6.8
The data EEPROM is a high endurance, byte address-
able array that has been optimized for the storage of
frequently changing information (e.g., program vari-
ables 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, cali-
bration, etc.) should be stored in FLASH program
memory.
A simple data EEPROM refresh routine is shown in
Example 6-3.
Note:
Operation During Code Protect
Using the Data EEPROM
If data EEPROM is only used to store con-
stants and/or data that changes rarely, an
array refresh is likely not required. See
specification D124.
© 2006 Microchip Technology Inc.