(6) PROGRAM STATUS WARD (PSW)

The program status ward is made up of the various flags which are
set and reset according to the results of the execution of 8-bit
register commads and the various flags which determine the
activities of the CPU. When reset it veocnes "000-0-00".

    7    6     5     4     3     2     1     0
  -----------------------------------------------
 |   N    V     P     -     H     -     Z     C  |
  ----------------------------------------------

Carry Flag (C).

After operation execution, this is set when there has been a carry
from the uppermost bit of the arithmetic logic unit (ALU) or when
there has been no borrow. It is even altered with shift or rotate
commands. It also acts as an bit accumulator of Boolean bit operation
commands. It is set at the SETC commads and reset at the CLRC commads.
In addition, the carry flag inverts at the NOTC commads.

Zero Flag (Z)

Alter operation execution, this flag is set when the result is
zero and is reset whens the result is not zero. Even with 16-bity
operation commands, zero detection is carried out. It is possible
to carry out tests with conditional branching commands.

Half Carry Flag (H)

After operation execution, this flag is set when there has been
a carry from form bit 3 of the ALU to bit 4, or when there has
not been any borrow. There is no command to set, however, it is
reset by reset by means of the CLRV commad. At his time, the
overflow flag is also set.

Direct Page Flag (P)

This is the flaq which designates the direct page to which many
addressing mode are applicable, such as direct page addressing
etc. When 0, the direct page becomes the addresses of the
region 0000-00ff and when 1, it becomes the addresses of the
region 0100-01ff. It is set by the STEP command and reset by the
CLRP command.

Overflow Flag (V).

After arithmetic operation execution, this flag is set when
overflow or underflow has been produced. At this time, influence
is extended simultaneously to the H flag.
It is possible to carry out tests with conditional branching 
commads.

Negative Flag (N)

After operation execution, this flag is set when the values of
the result of MSD is 1 and reset when that values is 0. It is
possible to carry out tests with conditinal branching commads.