Hi,
SUBB subtracts the indicated variable and the carry flag together from acc, leaving the result in the acc.SUBB sets the carry (borrow) flag if a borrow is needed for the bit 7 and clears C otherwise..."

Where it will go ? Label_1 or Label_2 ? Thanks.
...it will go to label 2

I guess you need to use a IDE like KEIL,its got a simulator...its available for free(eval) at http://www.keil.com

Rgds
Raj Shetgar