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PIC16F84A Datasheet(PDF) 35 Page - Microchip Technology |
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PIC16F84A Datasheet(HTML) 35 Page - Microchip Technology |
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35 / 124 page  PIC16F8X © 1998 Microchip Technology Inc. DS30430C-page 35 7.5 Write Verify Depending on the application, good programming practice may dictate that the value written to the Data EEPROM should be verified (Example 7-1) to the desired value to be written. This should be used in applications where an EEPROM bit will be stressed near the specification limit. The Total Endurance disk will help determine your comfort level. Generally the EEPROM write failure will be a bit which was written as a '1', but reads back as a '0' (due to leakage off the bit). EXAMPLE 7-1: WRITE VERIFY BCF STATUS, RP0 ; Bank 0 : ; Any code can go here : ; MOVF EEDATA, W ; Must be in Bank 0 BSF STATUS, RP0 ; Bank 1 READ BSF EECON1, RD ; YES, Read the ; value written BCF STATUS, RP0 ; Bank 0 ; ; Is the value written (in W reg) and ; read (in EEDATA) the same? ; SUBWF EEDATA, W ; BTFSS STATUS, Z ; Is difference 0? GOTO WRITE_ERR ; NO, Write error : ; YES, Good write : ; Continue program 7.6 Protection Against Spurious Writes 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, WREN 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. 7.7 Data EEPROM Operation during Code Protect When the device is code protected, the CPU is able to read and write unscrambled data to the Data EEPROM. For ROM devices, there are two code protection bits (Section 8.1). One for the ROM program memory and one for the Data EEPROM memory. TABLE 7-1 REGISTERS/BITS ASSOCIATED WITH DATA EEPROM Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Value on Power-on Reset Value on all other resets 08h EEDATA EEPROM data register xxxx xxxx uuuu uuuu 09h EEADR EEPROM address register xxxx xxxx uuuu uuuu 88h EECON1 — — — EEIF WRERR WREN WR RD ---0 x000 ---0 q000 89h EECON2 EEPROM control register 2 ---- ---- ---- ---- Legend: x = unknown, u = unchanged, - = unimplemented read as '0', q = value depends upon condition. Shaded cells are not used by Data EEPROM. |
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