What are various status stages provided in 8085? Discuss their role.
Answer:
8085 microprocessor provides five
status stages.
i.
The carry flag (cy)
ii.
The auxiliary carry
flag (p)
iii.
The parity status
flag (Ac)
iv.
The zero flag
v.
The sign status
flag.
Role of above five status
stages:-
*The carry Flag:- (Cy)
Reflects the final carry out of the
most significant bit of any arithmetic operation. Any logic instruction resets
or cleans the carry flag. This flag is also used by the shift and rotate
instructions. The 8085 does not have any “clear carry” instruction one way of
clearing the carry will be by oring or awing the accumulator with itself.
*The Parity status flag:- (P)
In set to 1 an arithmetic or logic
instruction generates an answer with even parity, that is containing an even
number of 1 bits. This flag is 0 if the arithmetic or logic instruction
generates an answer with odd parity that is, containing an odd number of 1 s.
*The auxiliary carry flag:- (Ac)
Reflects any carry from
bit 3 to bit 4 ( assuming 8- bit data with bit 0 as the least significant bit
and bit 7 as the most significant bit) due to an arithmetic operation. This
flag is useful for BCD operation.
*The zero flag:- (z)
Is set to 1 whenever an
arithmetic or logic operation produces a result of 0. The zero flag is cleared
to zero for a non-zero result due to arithmetic or logic operation.
*The sign status flag:- (S)
Is set to the value of the most
significant bit of the result in the accumulator after an arithmetic or logic
operation. This provides a range of -12810 to + 12710 (
with or being considered positive) as the 8085’s data-handling capacity.
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