Nowhere do you setup the stack pointer - so it normally resets to address 8 (from my memory). AS to whether your problem is caused by stack problems - try using a simulator. Then you'll see what you code is doing.

Just some advice - learn how to use memory to store your variables - your code is starting to get unmanageable relying on fixed registers.

Without reformatting your code I had trouble trying to follow the logic. The comments weren't too bad, but the structure left a lot to be desired.

Also write some string routines - makes printing stuff easier!
;
; DPTR-> string in rom terminated by 0x00
; prints string to ????
; zaps DPTR,A
;
pstring
clr a
movc a,@a+dptr ;grab char
jz ps_end ;exit if char == 0x00
call pchar ;output the char
inc dptr ;->++
sjmp pstring

ps_end
ret



printing a string then becomes:

mov dptr,#msg_ok
call pstring


msg_ok db 'Ok',0