Writing to EEPROM on PIC
Solution 1
On page 122 of the 16F690 datasheet, it details the proper way to write to EEPROM:
BANKSEL EEADR ; MOVF DATA_EE_ADDR, W; MOVWF EEADR ;Data Memory Address to write MOVF DATA_EE_DATA, W; MOVWF EEDAT ;Data Memory Value to write BANKSEL EECON1 ; BCF EECON1, EEPGD ;Point to DATA memory BSF EECON1, WREN ;Enable writes BCF INTCON, GIE ;Disable INTs. BTFSC INTCON, GIE ;SEE AN576 GOTO $-2 ; BEGIN REQUIRED SEQUENCE MOVLW 55h ; MOVWF EECON2 ;Write 55h MOVLW AAh ; MOVWF EECON2 ;Write AAh BSF EECON1, WR ;Set WR bit to begin write BSF INTCON, GIE ;Enable INTs. SLEEP ;Wait for interrupt to signal write complete ; END REQUIRED SEQUENCE BCF EECON1, WREN ;Disable writes BANKSEL 0x00 ;Bank 0
I noticed that you are specifically missing this line:
BCF EECON1, EEPGD ;Point to DATA memory
If EEPGD
is always set, then you'll try to write to program memory (aka overwrite the flash program memory) which should always fail unless you've gone out of your way to specifically enable that.
Aside from that, as far as I can tell from reading your code, everything else looks fine. It's okay that you're polling EECON1.WR
instead of setting an interrupt. It will cost you more power than putting the device to sleep, but of course you should just worry about one thing at a time.
Solution 2
If you use the high tech compiler, writing to EEPROM is as simple as
#include <pic.h>
and then in main,
EEPROM_WRITE(0, 0x00);
or really;
EEPROM_WRITE(location to write to, value to write to it);
I actually haven't been brave enough to write my PIC in assembly.
jcoder
Updated on June 04, 2022Comments
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jcoder about 2 years
Are there any PIC microcontroller programmers here?
I'm learning some PIC microcontroller programming using a pickit2 and the 16F690 chip that came with it. I'm working through trying out the various facilities at the moment. I can sucessfully read a byte from the EEPROM in code if I set the EEPROM vaklue in MPLAB but I don't seem to be able to modify the value using the PIC itsself. Simply nothing happens and I don't read back the modified value, I always get the original which implies to me that the write isn't working?
This is my code for that section, am I missing something? I know I'm doing a lot of unnecessary bank switches, I added most of them to ensure that being on the wrong bank wasn't the issue.
; ------------------------------------------------------ ; Now SET the EEPROM location ZERO to 0x08 ; ------------------------------------------------------ BANKSEL EEADR CLRF EEADR ; Set EE Address to zero BANKSEL EEDAT MOVLW 0x08 ; Store the value 0x08 in the EEPROM MOVWF EEDAT BANKSEL EECON1 BSF EECON1, WREN ; Enable writes to the EEPROM BANKSEL EECON2 MOVLW 0x55 ; Do the thing we have to do so MOVWF EECON2 ; that writes can work MOVLW 0xAA MOVWF EECON2 BANKSEL EECON1 BSF EECON1, WR ; And finally perform the write WAIT BTFSC EECON1, WR ; Wait for write to finish GOTO WAIT BANKSEL PORTC ; Just to make sure we are on the right bank
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jcoder about 14 yearsI'm clearin EEPGD in the previous code that sucessfully reads from the EEPROM and forgot to do it again here, but it should still be set to 0. Just in case I added and it still isn't working. Is there anything I need to set in my control flags or anything like that that I might have missed to allow writing?
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jcoder about 14 yearsAnd yes, I'm still learning and I've not got as far as learning interrupts yet, that and timers are next on my list.
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jcoder about 14 yearsAccepted this answer because it's correct and points out a small mistake in my code. I've got this to work by removing the unneeded back select statements. It seems that doing that in the middle of the programming sequence actually stops it working
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John Slegers about 14 yearsSection 10.1.3 of the datasheet also says "Interrupts should be disabled during this code segment.", referring to the "required sequence" in the code sample. Have you tried that?
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jcoder about 14 yearsI can't edit my comment above. I meant "bank" select, not "back" select. I don't have interrupts enabled in my program so no need to disable them. I have it working now anyway but thanks for the suggestion