table using pcl

jijita · Sep 2, 2004

i'm using 16f877 and i want to make a table using pcl:
movlw number
addwf pcl
retlw ...
retlw...
and you know the table i want is bigger than 256and i was wondering what is the method to increase the table elements when pcl becomes 256
i think i should increment pclath or something like that
could you help me i'd appreciate it if you could write a little piece of code to help me
thanks
and maybe if there's another method to do tables with 16f877 assembly

Exo · Sep 2, 2004

I use this code - Load the full address to lookup into AdrHi - AdrLo and then call lookup. It increases
the address every time Lookup is called and returns the data in W

Code:

Lookup

	CALL		Dummy			;A dummy call - Puts this adress on the stack to return to
	
	INCF		AdrLo, F		;the table's RETLW returns here with data in W - now increase address
	BTFSC	  STATUS, Z		
	INCF		AdrHi, F
	RETURN

Dummy	
	
	MOVF		AdrHi, W
	MOVWF	  PCLATH		;prewrite PCLATH...
	MOVF		AdrLo, W
	MOVWF	  PCL			;and write PCL - This jumps to table adress - There should be a RETLW there

Now for an example on how to call it:

Code:

	MOVLW	  HIGH(String)
	MOVWF	  AdrHi			;load high byte of lookup table's address
	MOVLW	  Low(String)
	MOVWF	  AdrLo			;load low byte of lookup table's address

GetNext

	CALL		Lookup			 ;and call Lookup - this returns the data on AdrHi-AdrLo in W
	MOVWF	  Scratch			;save W
	MOVF	   Scratch, W		;and move it back to W (modifies Z flag)
	BTFSC	  STATUS, Z;		;result is Z?
	GOTO 	  End			    ;yes? then end

	;Do something with the byte here!

	GOTO		GetNext

End	;Code ends here

String 	db	"This is a test!",0		;the lookup table!

jijita · Sep 3, 2004

thank you for the code

table using pcl

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