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    參數(shù)資料
    型號: PIC16C74A-04/PT
    廠商: Microchip Technology
    文件頁數(shù): 9/114頁
    文件大?。?/td> 0K
    描述: IC MCU OTP 4KX14 A/D PWM 44TQFP
    標準包裝: 160
    系列: PIC® 16C
    核心處理器: PIC
    芯體尺寸: 8-位
    速度: 4MHz
    連通性: I²C,SPI,UART/USART
    外圍設備: 欠壓檢測/復位,POR,PWM,WDT
    輸入/輸出數(shù): 33
    程序存儲器容量: 7KB(4K x 14)
    程序存儲器類型: OTP
    RAM 容量: 192 x 8
    電壓 - 電源 (Vcc/Vdd): 4 V ~ 6 V
    數(shù)據(jù)轉換器: A/D 8x8b
    振蕩器型: 外部
    工作溫度: 0°C ~ 70°C
    封裝/外殼: 44-TQFP
    包裝: 托盤
    PIC16C7X
    DS30390E-page 106
    1997 Microchip Technology Inc.
    12.2
    USART Asynchronous Mode
    In this mode, the USART uses standard nonreturn-to-
    zero (NRZ) format (one start bit, eight or nine data bits
    and one stop bit). The most common data format is
    8-bits. An on-chip dedicated 8-bit baud rate generator
    can be used to derive standard baud rate frequencies
    from the oscillator. The USART transmits and receives
    the LSb first. The USART’s transmitter and receiver are
    functionally independent but use the same data format
    and baud rate. The baud rate generator produces a
    clock either x16 or x64 of the bit shift rate, depending
    on bit BRGH (TXSTA<2>). Parity is not supported by
    the hardware, but can be implemented in software (and
    stored as the ninth data bit). Asynchronous mode is
    stopped during SLEEP.
    Asynchronous mode is selected by clearing bit SYNC
    (TXSTA<4>).
    The USART Asynchronous module consists of the fol-
    lowing important elements:
    Baud Rate Generator
    Sampling Circuit
    Asynchronous Transmitter
    Asynchronous Receiver
    12.2.1
    USART ASYNCHRONOUS TRANSMITTER
    The USART transmitter block diagram is shown in
    Figure 12-7. The heart of the transmitter is the transmit
    (serial) shift register (TSR). The shift register obtains its
    data from the read/write transmit buffer, TXREG. The
    TXREG register is loaded with data in software. The
    TSR register is not loaded until the STOP bit has been
    transmitted from the previous load. As soon as the
    STOP bit is transmitted, the TSR is loaded with new
    data from the TXREG register (if available). Once the
    TXREG register transfers the data to the TSR register
    (occurs in one TCY), the TXREG register is empty and
    Applicable Devices
    72 73 73A 74 74A 76 77
    ag bit TXIF (PIR1<4>) is set. This interrupt can be
    enabled/disabled by setting/clearing enable bit TXIE
    ( PIE1<4>). Flag bit TXIF will be set regardless of the
    state of enable bit TXIE and cannot be cleared in soft-
    ware. It will reset only when new data is loaded into the
    TXREG register. While ag bit TXIF indicated the sta-
    tus of the TXREG register, another bit TRMT
    (TXSTA<1>) shows the status of the TSR register. Sta-
    tus bit TRMT is a read only bit which is set when the
    TSR register is empty. No interrupt logic is tied to this
    bit, so the user has to poll this bit in order to determine
    if the TSR register is empty.
    Transmission is enabled by setting enable bit TXEN
    (TXSTA<5>). The actual transmission will not occur
    until the TXREG register has been loaded with data
    and the baud rate generator (BRG) has produced a
    shift clock (Figure 12-7). The transmission can also be
    started by rst loading the TXREG register and then
    setting enable bit TXEN. Normally when transmission
    is rst started, the TSR register is empty, so a transfer
    to the TXREG register will result in an immediate trans-
    fer to TSR resulting in an empty TXREG. A back-to-
    back transfer is thus possible (Figure 12-9). Clearing
    enable bit TXEN during a transmission will cause the
    transmission to be aborted and will reset the transmit-
    ter. As a result the RC6/TX/CK pin will revert to hi-
    impedance.
    In order to select 9-bit transmission, transmit bit TX9
    (TXSTA<6>) should be set and the ninth bit should be
    written to TX9D (TXSTA<0>). The ninth bit must be
    written before writing the 8-bit data to the TXREG reg-
    ister. This is because a data write to the TXREG regis-
    ter can result in an immediate transfer of the data to the
    TSR register (if the TSR is empty). In such a case, an
    incorrect ninth data bit maybe loaded in the TSR regis-
    ter.
    Note 1: The TSR register is not mapped in data
    memory so it is not available to the user.
    Note 2: Flag bit TXIF is set when enable bit TXEN
    is set.
    FIGURE 12-7: USART TRANSMIT BLOCK DIAGRAM
    TXIF
    TXIE
    Interrupt
    TXEN
    Baud Rate CLK
    SPBRG
    Baud Rate Generator
    TX9D
    MSb
    LSb
    Data Bus
    TXREG register
    TSR register
    (8)
    0
    TX9
    TRMT
    SPEN
    RC6/TX/CK pin
    Pin Buffer
    and Control
    8
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