Serial EEPROM Solutions vs. Parallel Solutions - The cost break even point for serial I2C non-volitile memory from useing multiple 32kx8 EEPROMs to using parallel flash memory with an I2C controller is at about 128k as of late 1999.
Ian Chapman <pic@chapmip.demon.co.uk> says:
BTW, I've just spotted an interesting point in AN709 about I2C EEPROMs which can power up in an incorrect state. The following initialisation sequence after power-up is recommended to resolve this:
- START bit
- Clock in nine bits of '1'
- START bit
- STOP bit
I haven't seen this in any examples of I2C master code before, but AN709 gives a good explanation of why it is needed to avoid the possibility of an erroneous write to the EEPROM.
Extending lifetime and reliability in EEPROMs
See also:
See:
Code:
This code will write the EEPROM on the 16F628 in chunks.
;
; Written: 14-Apr-2002, Chuck McManis
;
; Uses the temporary variable EE_LEN, EE_SRC, and EE_DST
; During write Source is RAM and Destination is EEPROM
;
; Note: Due to a bug in the 16F628 you can "overrun" the ability
; of the chip to write the EEPROM if you just monitor the WR bit
; in EECON1 (if you write immediately after it goes low the EEPROM
; may not be written.
;
; Thus this macro assumes that when it starts there is not a write
; currently in progress!
;
; Usage: EEWRITE <data bytes address (0-0xff)>, <eeprom address>, <len>
;
; On the 16F628, EE_LEN, EE_SRC, and EE_DST should be in the range
; 0x70 - 0x7F (mirrored on all ram banks)
;
;
EEWRITE MACRO SRC_ADDR, DST_ADDR, LEN
LOCAL WLOOP
MOVLW LEN ; Get length
MOVWF EE_LEN ; Store it in count
MOVLW SRC_ADDR ; Get the source address
MOVWF EE_SRC ; Store in the source addr
MOVLW DST_ADDR ; EEPROM Destination address
MOVWF EE_DST ; Store it too
WLOOP:
BCF PIR1, EEIF ; Clear this flag...
MOVF EE_SRC,W ; Source Address
MOVWF FSR ; Store in FSR
MOVF INDF,W ; Get a data byte
BSF STATUS, RP0 ; Switch to Bank 1
MOVWF EEDATA ; Store the data byte in EE Data
MOVF EE_DST,W ; Get the destination address
MOVWF EEADR ; .. this byte goes here
BSF EECON1, WREN ; Enable Writes to EEPROM
; BTFSS EECON1, WR ; This should work but doesn't (see
; GOTO $-1 ; below) it only writes 2 of n bytes.
BCF INTCON, GIE ; Interrupts off.
MOVLW H'55' ; Magic Sequence (Sequence Start)
MOVWF EECON2 ; ...
MOVLW H'AA' ; ...
MOVWF EECON2 ; ...
BSF EECON1, WR ; and Write it! (Sequence End)
BSF INTCON, GIE ; Interrupts are allowed again.
BCF EECON1, WREN ; Disable future writes.
BCF STATUS, RP0 ; back to bank 0
BTFSS PIR1, EEIF ; Wait for it to finish, this slows
GOTO $-1 ; ... us down! (bug! see above)
INCF EE_SRC, F ; Add 1 to source and destination
INCF EE_DST, F ; ... addresses (no overlap)
DECFSZ EE_LEN,F ; Decrement the length and ...
GOTO WLOOP ; ... loop if non-zero.
ENDM
For another example of reading the EEPROM, see PIC 16F876 full initialization sample program /techref/microchip/16f877/snipp.htm .
Questions:
file: /Techref/mem/eeproms.htm, 9KB, , updated: 2013/7/22 16:09, local time: 2024/12/25 00:09,
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