it seems you use C-language,

but why, why, why, do you manipulate with registers directly from C-language???
Lines like next:

DPH = u_add; 
DPL = l_add;

ACC = DPL; 
SPDR = ACC;

have no mean in the whole!!! Compiler and optimizer use the all registers by own way and even you wrote

DPL = l_add;
//...
ACC = DPL;

it DOES NEVER mean that ACC will be loaded with l_add finally. And even it is loaded, nevertheless it does not mean that at next step ACC will still contain this value.
Do not mix ASM and C-language. If you REALLY need with ASM then create separate .asm file.

As about your code - it is wrong due reason I indicated above. Under C-language, you must never rely on fact that MCU registers contain what you load into them. C-language does know nothing about regitsters and cannot operate with them from program directly at point of wiev of end-user (programmer).

Regards,
Oleg