first, thank you all for the enlightment!

there was one extra pop in my example, but that was due the late (2am) hour that I was writing :-)
A little bit that I don't understood:
"For using push & pop first you must set the value of stack pointer " set the SP? but the SP isn't independet from my code? I can set it to a given value? I never did that kind of manipulation... my needs are (were...) very simple... my code used to stay at 200 bytes... now I'm doing a code for a small robot that is already at 1k, so I must learn new tricks to do the job... and what value should I set the SP? The number of push'es plus the current SP?

to erik: I think that your example has shown my problem... I don't remember if I was push'ing and pop'ing in the same order! I will rewrite my code using your method and see what happens...

thank you all!