Erik pointed out that you call a subroutine (ETC_IAT) that appears to end in a jump rather than a return.

If this is the case, (and I am not sure that it is) then by calling but not returning, you are incrementing the stack by 2 every time. This unbalanced operation will eventually cause your stack to wrap around and overwrite registers with data in them. Or worse, the stack will be overwritten by data, and the next time you return, the processor will crash.

Your code needs a lot more comments, especially if you go to a forum for help. Ideally, every line is commented, and there are blocks of comments with every subroutine or functional block of code. Not only do the comments help others help you, they are very good for helping you to organize your own thoughts.

Here is a piece of your code, as provided

ECT: 
; write ect to pot 
mov a,r5 
clr cs 
acall txsend 
mov a,#pota 
acall txsend 
; acall delay 
setb cs 
ret 

And here it is with documentation

;---------------------------------------
;
;	ECT Subroutine - write ect value to external pot A
;
ECT: 
	mov	a, r5		; Fetch pot0 data
	clr	cs		; Bring /CS low
	acall	txsend		; Send code to digipot
	mov	a, #pota	; Code for selecting pota
	acall	txsend		; Send Code to digipot 
;	acall	delay		; Write delay 
	setb	cs		; Restore /CS
	ret 			; Return

Now, these comments may not be correct, and I may not be understanding what you are trying to do. Still, I think you will agree that it is easier to read. And that means it is much more likely to bring you meaningful help.