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  • 參數(shù)資料
    型號: MC68HC05SB7
    廠商: FREESCALE SEMICONDUCTOR INC
    元件分類: 微控制器/微處理器
    英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PDSO28
    封裝: MO-150, SSOP-28
    文件頁數(shù): 93/170頁
    文件大?。?/td> 2161K
    代理商: MC68HC05SB7
    August 27, 1998
    GENERAL RELEASE SPECIFICATION
    MC68HC05SB7
    CENTRAL PROCESSING UNIT
    MOTOROLA
    REV 2.1
    3-3
    Normally, the address in the program counter increments to the next sequential
    memory location every time an instruction or operand is fetched. Jump, branch,
    and interrupt operations load the program counter with an address other than that
    of the next sequential location.
    3.6
    CONDITION CODE REGISTER (CCR)
    The CCR shown in Figure 3-1 is a 5-bit register in which four bits are used to
    indicate the results of the instruction just executed. The fth bit is the interrupt
    mask. These bits can be individually tested by a program, and specic actions can
    be taken as a result of their states. The condition code register should be thought
    of as having three additional upper bits that are always ones. Only the interrupt
    mask is affected by a reset of the device. The following paragraphs explain the
    functions of the lower ve bits of the condition code register.
    3.6.1 Half Carry Bit (H-Bit)
    When the half-carry bit is set, it means that a carry occurred between bits 3 and 4
    of the accumulator during the last ADD or ADC (add with carry) operation. The
    half-carry bit is required for binary-coded decimal (BCD) arithmetic operations.
    3.6.2 Interrupt Mask (I-Bit)
    When the interrupt mask is set, the internal and external interrupts are disabled.
    Interrupts are enabled when the interrupt mask is cleared. When an interrupt
    occurs, the interrupt mask is automatically set after the CPU registers are saved
    on the stack, but before the interrupt vector is fetched. If an interrupt request
    occurs while the interrupt mask is set, the interrupt request is latched. Normally,
    the interrupt is processed as soon as the interrupt mask is cleared.
    A return from interrupt (RTI) instruction pulls the CPU registers from the stack,
    restoring the interrupt mask to its state before the interrupt was encountered. After
    any reset, the interrupt mask is set and can only be cleared by the Clear I-Bit
    (CLI), or WAIT instructions.
    3.6.3 Negative Bit (N-Bit)
    The negative bit is set when the result of the last arithmetic operation, logical
    operation, or data manipulation was negative. (Bit 7 of the result was a logical
    one.)
    The negative bit can also be used to check an often tested ag by assigning the
    ag to bit 7 of a register or memory location. Loading the accumulator with the
    contents of that register or location then sets or clears the negative bit according
    to the state of the ag.
    3.6.4 Zero Bit (Z-Bit)
    The zero bit is set when the result of the last arithmetic operation, logical
    operation, data manipulation, or data load operation was zero.
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