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    SCI LECTURE

    Dung Nguyen

    Joseph GlasoferAlan Carr

    ME 4447March 27, 2002

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    What is SCI ?

    SCI is an acronym for Serial

    Communication Interface

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    SCI Block Diagram

    RxD Receive Data Line (PD0)

    TxD Transmit Data Line (PD1)

    Access through port D in our case

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    SCI Block Diagram Cont

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    Serial Data Communication

    Type of data transmissions

    Mode of data communications Data transmission rates

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    Type of Data Transmission

    There are two types of data transmission

    Parallel data transmission

    Serial data transmission

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    Parallel Data Transmission

    Parallel

    Simultaneous 8-bit transmission

    Requires 16 data lines

    Transmitter uses 8 data lines

    Receiver uses 8 data lines

    Faster than serial transmission

    Expensive

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    Serial Data Transmission

    SerialTransfers 1 bit at a time

    Requires two data lines

    One line for the transmitter

    One line for the receiver

    Can be used to connect to a terminal or PC

    Slower than the parallel

    Low cost

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    Mode Of Data Communications

    There are two modes of data communications

    Synchronous Data Communications

    Asynchronous Data Communications

    They refer to the type of clocking used to

    transfer the data.

    h

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    Synchronous Data

    Communications

    Data words are locked into the systemclocking

    Receiver and Transmitter must besynchronized because there is no two-waycommunication

    Usually, one device will request some data

    from other device, wait a fixed period, andthen read or transmit the data

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    Asynchronous Data

    Communications

    Data words are not locked into the system

    clocking

    Start and Stop bits are added into the

    transmitter and receiver

    If the receiver detects the stop bit (end of

    data word), it will then wait for the next

    data word.

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    Data Transmission Rate

    There are two common terms used in serial datacommunication.

    Those are Baud rate and the bit rate.

    Do not confuse the Baud rate with the Bitrate, they are not the same.

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    Baud Rate Vs Bit Rate

    The baud rate includes the all the data bits

    The bit rate only includes the parity, and

    information bits

    See example

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    Baud Rate Vs Bit rate Example

    Role of stop, start, and parity bits

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    Baud Rate Vs Bit rate Example Cont

    parityincludingbits/sec80BTRrate-Bitbits/sec80terbit/charac8/seccharacters10110BR

    10WRrate-Word

    1.E09.911ms/bit9.09)worddatabits#(T

    (TW)wordcharacteronetransmittoTime

    )(110(BR)rate-Baud

    secondcharacters

    1.01

    3

    )(09.91

    timebit1

    s

    ms

    s

    baud

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    Asynchronous Serial Transmission

    Data is transmitted one bit at a time

    Several types of bits are used to maintain

    the integrity between words, including:

    Start Bit

    Data Bit

    Stop Bit

    Parity Bit

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    Start Bit

    A bit that comes before every word

    Signals the receiver that a data word is

    about to be transmitted

    In the HC11, this is a low logic bit (a zero)

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    Data Bit

    The bits that make up a data word

    Either a high or low logic bit (a one or a

    zero)

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    Stop Bit

    Bit that comes after every data word

    Signals to the receiver that the data word is

    finished

    For the HC11, this is a high logic bit (a one)

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    Parity Bit

    This is a bit before the stop bit

    Maintains the integrity of the word

    Counts the number of ones in the data word,

    including the parity bit

    Is either set to odd or even

    Parity bit is used to prevent noise

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    Noise

    Noise is interference in the line

    Can cause the data word to be

    misinterpreted The parity bit can prevent a single noise

    signal in a data word, but would miss adouble noise signal.

    HC11 combats this by taking three samplesnear the middles of each bit

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    SCI Registers

    Port D ($1008)

    Port D Data Direction Register (DDRD -

    $1009)

    BAUD Rate Control Register (BAUD -

    $102B)

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    SCI Registers (cont.)

    SCI Control Register 1 (SCCR1 - $102C)

    SCI Control Register 2 (SCCR2 - $102D)

    SCI Status Register (SCSR - $102E)

    SCI Data Register (SCDR - $102F)

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    BAUD Rate Control Register

    E-clock is scaled by the SCP0-1 and SCR0-

    2 bits

    Other bits are empty or for factory use only

    TCLR RCKB0 SCP0SCP1 SCR2 SCR1 SCR0

    0134 26 57

    UU00 U0 00

    $102B

    RESET

    BAUD

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    SCI Control Register

    R8, T8 are ninth bit when the SCI is configured for

    nine bits

    M bit is to set SCI for 8 (0) or 9 (1) bits

    WAKE bit is the Wake-up Method Select bit

    R8 T8 0 M WAKE 0 0 0 $102CSCCR1

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    SCI Control Register (cont.)

    TIE stands for Transmit Interrupt Enable

    TCIE stands for Transmit Complete

    Interrupt Enable

    RIE stands for Receive Interrupt Enable

    ILIE stands for Idle-Interrupt Enable

    TIE TCIE RIE ILIE TE RE RWU SBK $102DSCCR2

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    SCI Control Register (cont.)

    TE stands for Transmit Enable

    RE stands for Receive Enable

    RWU stands for Receiver Wake Up

    SBK stands for Send Break

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    SCI Status Register

    TDRE stands for Transmit Data Register

    Empty

    TC stands for Transmit Complete

    RDRF stands for Receive Data Register

    Full

    TDRE TC RDRF IDLE OR NF FE 0SCSR $102E

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    SCI Status Register (cont.)

    IDLE stands for Idle-Line Detect

    OR stands for Overrun Error

    NF is the Noise Flag

    FE is the Framing Error

    0 Bit is empty

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    SCI Data Register

    Data Register used as two separate registers

    Read only RDR is accessed for Receiver

    mode

    Write only TDR is accessed for Transmitter

    Mode

    R7

    T7

    R6

    T6

    R5

    T5

    R4

    T4

    R3

    T3

    R2

    T2

    R1

    T1

    R0

    T0$102F

    SCDR

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    Transmitting Steps

    1. Set Baud rate to equal receiver

    2. Set TE (SCCR2) high to enable

    3. Set Wake Up mode (SCCR1)

    4. TE sends idle character to wake receiver5. Receiver determines if message is intended for it

    6. Load character into SCI Data Register (SCDR)

    7. Character placed in shift register and shifted out

    8. When TDRE (SCSR) sets back to 1, load another character (both

    polling and interrupts can be used).

    9. Transmission complete (TC in SCSR)

    10. Idle line rests at logic 1, RWU goes to 0

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    Receiving Steps

    1. Set Baud rate in Baud register ($102B)

    2. Set bit 4 in SCCR1 ($102C) to select 8 or 9 bit characters; set bit 3 to

    select wake up mode

    3. Set bit 2 in SCCR2 ($102D) to enable receiver; set bit 4 to enableinterrupt on idle; set bit 5 to enable interrupt when character received

    or overrun occurs.

    4. Read status of receive from SCSR ($102E) Bit 5 will be set when

    data is received; framing error sets bit 1; noise sets bit 2; overrun sets

    bit 3; idle sets bit 45. Read data received from SCDR ($102F)

    6. If 9 bit data format is used, the ninth bit of data will be located in bit

    7 of SCCR1 ($102C)