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  • 參數(shù)資料
    型號(hào): M38B49EBH-XXXXFP
    廠商: Mitsubishi Electric Corporation
    英文描述: SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
    中文描述: 單芯片8位CMOS微機(jī)
    文件頁(yè)數(shù): 61/78頁(yè)
    文件大?。?/td> 1214K
    代理商: M38B49EBH-XXXXFP
    61
    38B4 Group
    SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
    MITSUBISHI MICROCOMPUTERS
    CLOCK GENERATING CIRCUIT
    The 38B4 group has two built-in oscillation circuits. An oscillation
    circuit can be formed by connecting a resonator between X
    IN
    and
    X
    OUT
    (X
    CIN
    and X
    COUT
    ). Use the circuit constants in accordance with
    the resonator manufacturer’s recommended values. No
    external resistor is needed between X
    IN
    and X
    OUT
    since a feedback
    resistor exists on-chip. However, an external feedback resistor is
    needed between X
    CIN
    and X
    COUT
    .
    Immediately after power on, only the X
    IN
    oscillation circuit starts
    oscillating, and X
    CIN
    and X
    COUT
    pins function as I/O ports.
    Frequency Control
    (1) Middle-speed mode
    The internal system clock is the frequency of X
    IN
    divided by 4. After
    reset, this mode is selected.
    (2) High-speed mode
    The internal system clock is the frequency of X
    IN
    .
    (3) Low-speed mode
    The internal system clock is the frequency of X
    CIN
    divided by 2.
    I
    Note
    If you switch the mode between middle/high-speed and low-speed,
    stabilize both X
    IN
    and X
    CIN
    oscillations. The sufficient time is required
    for the sub clock to stabilize, especially immediately after power on
    and at returning from stop mode. When switching the mode between
    middle/high-speed and low-speed, set the frequency on condition
    that f(X
    IN
    ) > 3f(X
    CIN
    ).
    (4) Low power consumption mode
    The low power consumption operation can be realized by stopping
    the main clock X
    IN
    in low-speed mode. To stop the main clock, set bit
    5 of the CPU mode register to “1”. When the main clock X
    IN
    is re-
    started (by setting the main clock stop bit to “0”), set enough time for
    oscillation to stabilize.
    By clearing furthermore the X
    COUT
    drivability selection bit (b3) of CPU
    mode register to “0”, low power consumption operation of less than
    200 μA (f(X
    CIN
    ) = 32 kHz) can be realized by reducing the drivability
    between X
    CIN
    and X
    COUT
    . At reset or during STP instruction execu-
    tion this bit is set to “1” and a strong drivability that has an easy
    oscillation start is set.
    Oscillation Control
    (1) Stop mode
    If the STP instruction is executed, the internal system clock stops at
    an “H” level, and X
    IN
    and X
    CIN
    oscillators stop. Timer 1 is set to “FF
    16
    and timer 2 is set to “01
    16
    ”.
    Either X
    IN
    divided by 8 or X
    CIN
    divided by 16 is input to timer 1 as
    count source, and the output of timer 1 is connected to timer 2. The
    bits of the timer 12 mode register are cleared to “0”. Set the interrupt
    enable bits of the timer 1 and timer 2 to disabled (“0”) before execut-
    ing the STP instruction. Oscillator restarts when an external interrupt
    is received or reset, but the internal system clock is not supplied to
    the CPU until timer 1 underflows. This allows time for the clock cir-
    cuit oscillation to stabilize.
    (2) Wait mode
    If the WIT instruction is executed, the internal system clock stops at
    an “H” level. The states of X
    IN
    and X
    CIN
    are the same as the state
    before executing the WIT instruction. The internal system clock re-
    starts at reset or when an interrupt is received. Since the oscillator
    does not stop, normal operation can be started immediately after the
    clock is restarted.
    Fig. 71 Ceramic resonator circuit
    Fig. 72 External clock input circuit
    X
    C
    I
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    X
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    U
    T
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    C
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    U
    T
    R
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    R
    d
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    U
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    p
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