HMS81004E/08E/16E/24E/32E
18
JUNE 2001 Ver 1.00
[Zero flag Z]
This flag is set when the result of an arithmetic operation
or data transfer is "0" and is cleared by any other result.
Figure 8-4 PSW (Program Status Word) Register
[Interrupt disable flag I]
This flag enables/disables all interrupts except interrupt
caused by Reset or software BRK instruction. All inter-
rupts are disabled when cleared to "0". This flag immedi-
ately becomes "0" when an interrupt is served. It is set by
the EI instruction and cleared by the DI instruction.
[Half carry flag H]
After operation, this is set when there is a carry from bit 3
of ALU or there is no borrow from bit 4 of ALU. This bit
can not be set or cleared except CLRV instruction with
Overflow flag (V).
[Break flag B]
This flag is set by software BRK instruction to distinguish
BRK from TCALL instruction with the same vector ad-
dress.
[Direct page flag G]
This flag assigns RAM page for direct addressing mode. In
the direct addressing mode, addressing area is from zero
page 00
H
to 0FF
H
when this flag is "0". If it is set to "1",
addressing area is 1 Page. It is set by SETG instruction and
cleared by CLRG.
[Overflow flag V]
This flag is set to "1" when an overflow occurs as the result
of an arithmetic operation involving signs. An overflow
occurs when the result of an addition or subtraction ex-
ceeds +127(7F
H
) or -128(80
H
). The CLRV instruction
clears the overflow flag. There is no set instruction. When
the BIT instruction is executed, bit 6 of memory is copied
to this flag.
[Negative flag N]
This flag is set to match the sign bit (bit 7) status of the re-
sult of a data or arithmetic operation. When the BIT in-
struction is executed, bit 7 of memory is copied to this flag.
N
NEGATIVE FLAG
V
G
B
H
I
Z
C
MSB
LSB
RESET VALUE : 00
H
PSW
OVERFLOW FLAG
BRK FLAG
CARRY FLAG RECEIVES
CARRY OUT
ZERO FLAG
INTERRUPT ENABLE FLAG
HALF CARRY FLAG RECEIVES
CARRY OUT FROM BIT 1 OF
ADDITION OPERLANDS
SELECT DIRECT PAGE
when g=1, page is addressed by RPR