3858 Group
•Bit 4: Break flag (B)
[Processor status register (PS)]
The B flag is used to indicate that the current interrupt was
generated by the BRK instruction. The BRK flag in the processor
status register is always “0”. When the BRK instruction is used to
generate an interrupt, the processor status register is pushed
onto the stack with the break flag set to “1”.
The processor status register is an 8-bit register consisting of 5
flags which indicate the status of the processor after an arithmetic
operation and 3 flags which decide MCU operation. Branch opera-
tions can be performed by testing the Carry (C) flag , Zero (Z) flag,
Overflow (V) flag, or the Negative (N) flag. In decimal mode, the Z,
V, N flags are not valid.
•Bit 5: Index X mode flag (T)
When the T flag is “0”, arithmetic operations are performed
between accumulator and memory. When the T flag is “1”, direct
arithmetic operations and direct data transfers are enabled
between memory locations.
•Bit 0: Carry flag (C)
The C flag contains a carry or borrow generated by the arithmetic
logic unit (ALU) immediately after an arithmetic operation. It can
also be changed by a shift or rotate instruction.
•Bit 1: Zero flag (Z)
•Bit 6: Overflow flag (V)
The V flag is used during the addition or subtraction of one byte
of signed data. It is set if the result exceeds +127 to -128. When
the BIT instruction is executed, bit 6 of the memory location
operated on by the BIT instruction is stored in the overflow flag.
•Bit 7: Negative flag (N)
The Z flag is set if the result of an immediate arithmetic operation
or a data transfer is “0”, and cleared if the result is anything other
than “0”.
•Bit 2: Interrupt disable flag (I)
The I flag disables all interrupts except for the interrupt
generated by the BRK instruction.
The N flag is set if the result of an arithmetic operation or data
transfer is negative. When the BIT instruction is executed, bit 7 of
the memory location operated on by the BIT instruction is stored
in the negative flag.
Interrupts are disabled when the I flag is “1”.
•Bit 3: Decimal mode flag (D)
The D flag determines whether additions and subtractions are
executed in binary or decimal. Binary arithmetic is executed when
this flag is “0”; decimal arithmetic is executed when it is “1”.
Decimal correction is automatic in decimal mode. Only the ADC
and SBC instructions can be used for decimal arithmetic.
Table 4 Set and clear instructions of each bit of processor status register
C flag
Z flag
I flag
D flag
B flag
T flag
V flag
_
N flag
_
_
_
_
_
_
Set instruction
SEC
CLC
SEI
CLI
SED
CLD
SET
CLT
Clear instruction
CLV
Rev.1.10 Apr 3, 2006 page 8 of 75
REJ03B0139-0110
RENESAS [ RENESAS TECHNOLOGY CORP ]
