參數(shù)資料
      型號(hào): M37548G2-XXXFP
      元件分類: 微控制器/微處理器
      英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDSO20
      封裝: 4.40 X 6.50 MM, 0.65 MM PITCH, PLASTIC, LSSOP-20
      文件頁數(shù): 4/86頁
      文件大?。?/td> 1437K
      代理商: M37548G2-XXXFP
      Rev.2.02
      Mar 31, 2009
      Page 10 of 81
      REJ03B0210-0202
      7548 Group
      [Processor status register (PS)]
      The processor status register is an 8-bit register consisting of flags
      which indicate the status of the processor after an arithmetic
      operation. Branch operations 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.
      After reset, the Interrupt disable (I) flag is set to “1”, but all other
      flags are undefined. Since the Index X mode (T) and Decimal
      mode (D) flags directly affect arithmetic operations, they should
      be initialized in the beginning of a program.
      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”.
      When an interrupt occurs, this flag is automatically set to “1”
      to prevent other interrupts from interfering until the current
      interrupt is serviced.
      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.
      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”. The saved processor status is the only place where the
      break flag is ever set.
      Bit 5: Index X mode flag (T)
      When the T flag is “0”, arithmetic operations are performed
      between accumulator and memory, e.g. the results of an
      operation between two memory locations is stored in the
      accumulator. When the T flag is “1”, direct arithmetic
      operations and direct data transfers are enabled between
      memory locations, i.e. between memory and memory,
      memory and I/O, and I/O and I/O. In this case, the result of
      an arithmetic operation performed on data in memory
      location 1 and memory location 2 is stored in memory
      location 1. The address of memory location 1 is specified by
      index register X, and the address of memory location 2 is
      specified by normal addressing modes.
      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.
      [CPU mode register] CPUM
      The CPU mode register contains the stack page selection bit.
      This register is allocated at address 003B16.
      Fig 7.
      Structure of CPU mode register
      The processor mode bits can be written only once after releasing reset.
      Always set them to “002”. After written, rewriting any data to these
      bits is disabled because they are locked. (Emulator MCU is excluded.)
      Also, the stack page selection bit (bit 2) is not locked.
      In order to prevent error-writing to the processor mode bits (at
      program runaway), write the CPU mode register at the start of
      the program that runs after releasing reset.
      Table 5
      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
      SEI
      SED
      SET
      Clear instruction
      CLC
      CLI
      CLD
      CLT
      CLV
      CPU mode register
      (CPUM: address 003B16, initial value: 0016)
      Processor mode bits
      b1b0
      0 0 :
      Single-chip mode
      0 1 :
      Not available
      1 0 :
      Not available
      1 1 :
      Not available
      Stack page selection bit
      0 : 0
      page
      1 : 1
      page
      Disable (returns “0” when read
      )
      b7
      b0
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