PIC16F690 EEPROM counter issue

Hey,

I've written a subroutine to increment a counter stored in EEPROM memory on a PIC16F690.

The routine reads the previous value, increments it and then writes the new value. The routine works but only if I have a delay greater than 200 ms between reading and writing the new value. If the delay isn't there, the value is incremented by 8 (or 6 or 14...not sure what determines the value).

I've copy and pasted my code below. Let me know what you think.

Thanks,
-Phil



#include <p16F690.inc>
__config (_INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_OFF & _MCLRE_OFF & _CP_OFF & _BOR_OFF & _IESO_OFF & _FCMEN_OFF)

cblock 0x20
Delay1 ; Assign an address to Delay variables
Delay2
Delay3
Delay4
DATA_EE_DATA
COUNT
COUNT2
COUNT3
endc

org 0

Start


;************************Initialize PORT A***************
BCF STATUS,RP0 ;Bank 0
BCF STATUS,RP1 ;
CLRF PORTA ;Init PORTA
BSF STATUS,RP1 ;Bank 2
CLRF ANSEL ;digital I/O
BSF STATUS,RP0 ;Bank 1
BCF STATUS,RP1 ;
MOVLW b'00000000' ;Port A all output
MOVWF TRISA
BCF STATUS,RP0 ;Bank 0

;************************Initialize PORT B****************
BCF STATUS,RP0 ;Bank 0
BCF STATUS,RP1 ;
CLRF PORTB ;Init PORTB
BSF STATUS,RP1 ;Bank 2
CLRF ANSELH ;digital I/O
BSF STATUS,RP0 ;Bank 1
MOVLW b'00000000' ; all output
MOVWF TRISB ;
BCF STATUS,RP0 ;Bank 0

;************************Initialize PORT C***************
BCF STATUS,RP0 ;Bank 0
BCF STATUS,RP1 ;
CLRF PORTC ;Init PORTC
BSF STATUS,RP1 ;Bank 2
CLRF ANSEL ;digital I/O
BSF STATUS,RP0 ;Bank 1
BCF STATUS,RP1 ;
MOVLW b'00000000'; all output.
MOVWF TRISC
BCF STATUS,RP0 ;Bank 0

;******************************************Read counter value

bsf PORTC,0

BANKSEL EEADR
MOVlw 05h;
MOVWF EEADR ;Data Memory
;Address to read
BANKSEL EECON1 ;
BCF EECON1, EEPGD ;Point to DATA memory
BSF EECON1, RD ;EE Read
BANKSEL EEDAT ;BANK 2
MOVF EEDAT, W ;W = EEDAT
banksel TMR0 ; BANK 0
movwf COUNT;





BSF PORTC,1 ;Turn an LED on

;********************************************Increment counter


INCF COUNT,1

;********************************************Write the new value

movlw 0x02
movwf Delay3

Readdelay
decfsz Delay1,f ;
goto Readdelay ; ~400ms delay
decfsz Delay2,f ;
goto Readdelay ; Without this delay, the values
decfsz Delay3,f ; are incremented by 8 rather than 1
goto Readdelay ;



BANKSEL EEADR ;Bank 2

movlw 05h;
MOVWF EEADR ;Data Memory Address to write

banksel TMR0 ;Bank 0
MOVF COUNT,0;

BANKSEL EEDAT ;Bank 2
MOVWF EEDAT ;Data Memory Value to write

BANKSEL EECON1 ;Bank 3
BCF EECON1, EEPGD ;Point to DATA memory
BSF EECON1, WREN ;Enable writes
BCF INTCON, GIE ;Disable INTs.
BTFSC INTCON, GIE ;SEE AN576
GOTO $-2
MOVLW 0x55 ;
MOVWF EECON2 ;Write 55h
MOVLW 0xAA ;
MOVWF EECON2 ;Write AAh
BSF EECON1, WR ;Set WR bit to begin write

Wait2 btfsc EECON1,WR ; Wait for write complete
goto Wait2
bcf EECON1,WREN ; Disable write

BCF EECON1, WREN ;Disable writes

banksel TMR0 ;Bank 0

bsf PORTC,2 ;Turn some LEDS on

bsf PORTC,3

bsf PORTC,1;


end

The EEPROM is not fast. 200 ms seem a lot, though.

Also, the EEPROM has a limited endurance!

Quasi-solved

I added a 400 ms delay at startup and an infinite wait loop at the end of the program. The program should complete once and wait in the loop at the end.



And tada. It works without the delay in between the read and write.



Thanks to Janni for his comments on the Microchip forum. I didn't realize that the EEPROM couldn't be written so soon after power on. The charge pump requires half a second or so to get the voltages high enough to erase/write?

The odd thing is that I would expect it to correct itself after a few write cycles as the voltage level increases. It just keeps incrementing by 8 no matter how long the chip is on.

The power-up timer (64 ms) should be enough. I didn't notice that it's disabled in your program.

Since the EEPROM is only supposed to be for long term storage of data, I would change the program a little bit to store the counter in the RAM. Then every few minutes or when the unit is finished, write to the EEPROM. That would increase its lifespan a lot.