dear Mak Kini

Here is the way I would maximize stack size
this is an extract from my floating point library


;======= Floating point variables ===========
float_arg equ 3 ;3 bytes mantissa
float_exp equ 1 ;1 byte exponent
expbias equ 128 ;exponent bias

Quo: ds float_arg ;holds quotient of divide
Aarg: ds float_arg
Aexp: ds float_exp
Barg: ds float_arg
Bexp: ds float_exp
Aext: ds 1 ;extension for Aarg
Aext2: ds 1 ;for holding the aligned bit
;======= Floating point variables ===========

TOS: ;Stack top. Stack grows upwards from here

If you need to know how much stack is available to your program while it is running, you may calculate by stack size = 256-TOS (for 8052)
stack size = 128-TOS (for 8051)

I hope this answers your query if I understood you correctly.

Jerson