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PIC18F2525 Datasheet(PDF) 78 Page - Microchip Technology |
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PIC18F2525 Datasheet(HTML) 78 Page - Microchip Technology |
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78 / 412 page  PIC18F2525/2620/4525/4620 DS39626E-page 76 © 2008 Microchip Technology Inc. 6.6 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 23.0 “Special Features of the CPU” for additional information. 6.7 Protection Against Spurious Write 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 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 Reset, power glitch or software malfunction. 6.8 Using the Data EEPROM 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 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 6-3. EXAMPLE 6-3: DATA EEPROM REFRESH ROUTINE Note: If data EEPROM is only used to store constants and/or data that changes often, an array refresh is likely not required. See specification D124. CLRF EEADR ; Start at address 0 CLRF EEADRH ; 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 0AAh ; MOVWF EECON2 ; Write 0AAh 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 INCFSZ EEADRH, F ; Increment the high address BRA LOOP ; Not zero, do it again BCF EECON1, WREN ; Disable writes BSF INTCON, GIE ; Enable interrupts |
Similar Part No. - PIC18F2525_08 |
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Similar Description - PIC18F2525_08 |
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