Re: Problems reading data EEprom on Pic 16F88

From: Sergio Masci (sergio_at_NO.SPAM.xcprod.com)
Date: 11/13/04

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    Date: Sat, 13 Nov 2004 18:31:14 -0000

    Simon <si767676@hotmail.com> wrote in message
    news:6c289e8a.0411130940.75fe5ac4@posting.google.com...
    > I have been trying to use the read data EEPROM feature of the 16F88,
    > but can't get it to work.
    >
    > I have used the sample code from Microchip's data***. Attached is
    > the (entire) ASM file that I am using. It should (I had hoped) store
    > the value h'BB' in the register count1. Then read it from the data
    > EEPROM location (h'20') and store it into the register count2.
    >
    > When I step through it in the simulator, the EEDATA register gets the
    > value h'FF' instead of h'BB'. I can't figure this out and have spent
    > many hours on it so would be very grateful if someone could help.
    >
    > Code follows...
    >
    >
    > LIST N=90,ST=OFF,p=16F88
    > INCLUDE P16f88.INC ;Register definitions
    > errorlevel 0,-302
    > __config _config1, _hs_osc & _wdt_off & _pwrte_on & _cp_off &
    > _boden_off & _CCP1_RB0 & _WRT_PROTECT_OFF & _CPD_OFF & _LVP_OFF
    > __config _config2, _IESO_ON & _FCMEN_ON
    >
    >
    > cblock h'20' ;
    > count1
    > count2
    > ADDR
    > endc
    >
    >
    > GOTO INITIALISE
    > NOP
    > NOP
    > NOP
    >
    > INITIALISE
    >
    > banksel eedata ; Clearing these registers first to make it easier
    > ; to see what's going on in Watch Window
    > clrf eedata
    > clrf eeadr
    >
    > banksel count1
    > clrf count1
    > clrf count2
    > movlw h'BB'
    > movwf count1
    >
    > read_eeprom ; This section of code taken from 16F88 data***
    > BANKSEL EEADR ; Select Bank of EEADR
    >
    > ; MOVF ADDR,W ; I replaced this line with the literal value
    > h'20'
    > movlw h'20' ; (which is the address of count1) for the
    > purposes of
    > ; troubleshooting
    >
    > MOVWF EEADR ; Data Memory Address to read
    > BANKSEL EECON1 ; Select Bank of EECON1
    > BCF EECON1,EEPGD ; Point to Data memory
    > BSF EECON1,RD ; EE Read
    > BANKSEL EEDATA ; Select Bank of EEDATA
    > MOVF EEDATA,W ; W = EEDATA
    >
    > ; check to see if data read successful
    > banksel count2
    > movwf count2 ; move the data value to count2
    >
    > goto $
    > end

    Hi Simon,

    The data EEPROM is protected from accidental corruption by use of a
    protocol. You need to write 0x55 and 0xAA to special function register
    before writing to the EEPROM. I cannot remember the details off the top of
    my head. Look at the 16f88 data ***, there are flowcharts and code samples
    that show you exactly what you should be doing. Read the explanation
    carefully.

    Regards
    Sergio Masci

    http://www.xcprod.com/titan/XCSB - optimising PIC compiler
    FREE for personal non-commercial use

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