参数资料
型号: M38514E6-XXXFP
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 4 MHz, MICROCONTROLLER, PDSO42
封装: 0.450 INCH, 0.80 MM PITCH, PLASTIC, SSOP-42
文件页数: 3/93页
文件大小: 1137K
代理商: M38514E6-XXXFP
Rev.1.01
Oct 15, 2003
page 9 of 89
3851 Group (Built-in 24 KB or more ROM)
Bit 4: Break flag (B)
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”.
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 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 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.
Table 6 Set and clear instructions of each bit of processor status register
Set instruction
Clear instruction
C flag
Z flag
I flag
D flag
B flag
T flag
V flag
N flag
SEC
CLC
_
SEI
CLI
SED
CLD
_
SET
CLT
CLV
_
[Processor status register (PS)]
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 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)
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.
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.
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