eeprom internal pic16f628

[neelam29]

dear all
m trying to use internal eeprom of pic16f628 to read and write data .this is the code below .m not getting the correct output .please help me find the mistake.

LIST	p=16F628a		;tell assembler what chip we are using
	include "P16F628a.inc"		;include the defaults for the chip
	ERRORLEVEL	0,	-302	;suppress bank selection messages
	__CONFIG _CP_OFF & _WDT_OFF & _INTRC_OSC_NOCLKOUT & _PWRTE_ON & _LVP_OFF & _BODEN_OFF & _MCLRE_OFF




		cblock	0x20			;start of general purpose registers
			count			;used in looping routines
			count1			;used in delay routine
			counta			;used in delay routine
			countb			;used in delay routine

			prom_ADDR
			prom_DATA

	
		endc



		org	0x0000

		movlw	0x07
		movwf	CMCON			;turn comparators off (make it like a 16F84)

Initialise	clrf	count
		clrf	PORTA
		clrf	PORTB
		clrf	prom_ADDR
		clrf	prom_DATA


SetPorts	bsf 	STATUS,		RP0	;select bank 1
		movlw	0x00			;make all pins outputs
		movwf	TRISA
		movwf	TRISB
		bcf 	STATUS,		RP0	;select bank 0

	


		call	Delay255
		call	Delay255
		call	Delay255
		call	Delay255


		movlw 	0x50
		movwf	prom_ADDR
		movlw 	0x12
		movwf	prom_DATA
		call	write_eeprom
		
		call 	Delay20




		movlw	0x50
		movwf	prom_ADDR
		call	read_eeprom

		movf	prom_DATA, w
		movwf	PORTB

stop	goto	stop

;Subroutines

write_eeprom

		BSF STATUS, RP0 ;Bank 1
		
		movlw 	prom_ADDR
		movwf	EEADR
		movf	prom_DATA, w
		movwf	EEDATA	
		
		BSF EECON1, WREN ;Enable write
		;BCF INTCON, GIE ;Disable INTs.
		MOVLW 0x55 ;
		MOVWF EECON2 ;Write 55h
		MOVLW 0xAA ;
		MOVWF EECON2 ;Write AAh
		BSF EECON1,WR ;Set WR bit
						;begin write
		;BSF INTCON, GIE ;Enable INTs.

		BCF 	STATUS, RP0 ;Bank 0
		retlw	0x00	








read_eeprom
		BSF 	STATUS, RP0 ;Bank 1
		MOVLW 	prom_ADDR 	;
		MOVWF 	EEADR ;Address to read
		BSF 	EECON1, RD ;EE Read
		MOVF 	EEDATA, W ;W = EEDATA
		movwf	prom_DATA
		BCF 	STATUS, RP0 ;Bank 0
		
		return




Delay255	movlw	0xff		;delay 255 mS
		goto	d0
Delay100	movlw	d'100'		;delay 100mS
		goto	d0
Delay50		movlw	d'50'		;delay 50mS
		goto	d0
Delay20		movlw	d'20'		;delay 20mS
		goto	d0
Delay5		movlw	0x05		;delay 5.000 ms (4 MHz clock)
d0		movwf	count1
d1		movlw	0xC7			;delay 1mS
		movwf	counta
		movlw	0x01
		movwf	countb
Delay_0
		decfsz	counta, f
		goto	$+2
		decfsz	countb, f
		goto	Delay_0

		decfsz	count1	,f
		goto	d1
		retlw	0x00



		end

 

[Pommie]

You have a couple of problem in your code. The main one is that your variables (prom_ADDR & prom_DATA) are in bank 0 but you are accessing them in bank 1.

This can be fixed a number of ways.
1. Move the variables to a location that appears in both banks. These are 0x70 to 0x7f.
2. Switch banks when accessing them.
I.E.

; assumed to be in bank 0
      movlw    prom_ADDR 
      BSF STATUS, RP0 ;Bank 1        
      movwf   EEADR 
      BCF STATUS, RP0 ;Bank 0
      movf   prom_DATA, w 
      BSF STATUS, RP0 ;Bank 1        
      movwf   EEDATA

Do the same in the read EEPROM.

3. Use a subroutine to setup address. You won't need the variables then.

      movlw 0x50h
      call  setaddress
      movlw 0x12
      call write_eeprom
      .
      .

setaddress
      BSF STATUS, RP0 ;Bank 1        
      movwf   EEADR 
      BCF STATUS, RP0 ;Bank 0
      return

write_eeprom
      BSF STATUS, RP0 ;Bank 1        
      movwf   EEDATA    
     .
     .

The other thing that may cause a problem is that you don't wait for the write to be completed. After you set the WR bit you should do something like.

                bsf    EECON1,WR
                bcf    STATUS,RP0
waitEEdone      btfss  PIR1,EEIF
                goto   waitEEdone
                bcf    PIR1,EEIF
                bsf    STATUS,RP0
                bcf    EECON1,WREN

You should also clear the WREN bit as shown above.

And lastly, it's a good idea to disable interrupts where indicated. If you don't then a very hard to find bug could come along later.

HTH


Mike.

 

[neelam29]

Thanks for your great help. Actually i'm very new to PIC programming, if you can please provide me a complete example of this (even a small one will do), i'll be really very thankful to you.

Thanks once again

 

[Pommie]

If you want complete examples, then have a look at

Mike.

 

[Mike - K8LH]

Speaking of tutorials, you may want to check out the Elmer 160 Tutorial for a decent A-to-Z tutorial series that also helps reinforce good programming practices...

Have fun... Regards, Mike

 

[neelam29]

Thanks a lot everyone. I was able to do it.