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    參數(shù)資料
    型號: T8532
    元件分類: Codec
    英文描述: T8502 and T8503 Dual PCM Codecs with Filters
    中文描述: T8502和T8503雙的PCM編解碼器與濾波器
    文件頁數(shù): 15/48頁
    文件大?。?/td> 999K
    代理商: T8532
    Lucent Technologies Inc.
    15
    Preliminary Data Sheet
    November 2000
    Codec Chip Set
    T8531/T8532 Multichannel Programmable
    Chip Set Functional Description
    (continued)
    T8531 Functional Blocks
    (continued)
    T8531 System Interface
    The system interface is a full-duplex interface used for
    the exchange of PCM data with the system. The sys-
    tem is the master of this bus. No control information is
    transmitted over the system interface; all control
    instructions are routed over the microprocessor inter-
    face.
    The system interface is used for all 16 lines serviced by
    the T8531. The PCM data rate is 8 ksamples/s/line,
    so the total required channel capacity is 16 x 8 =
    128 Kwords/s in each direction. At the 4.096 MHz rate,
    each word takes 1.95
    μ
    s to transmit interleaved with
    5.86
    μ
    s of dead time. The frame sync, SFS, is pre-
    sented to the system interface at an 8 kHz rate.
    A single bit clock and frame sync are used to control
    both the transmit and receive directions. The beginning
    of the first time slot in a frame is identified from the SFS
    input (see Figure 9). In nondelayed mode, SFS is
    active coincident with bit 0 of time slot 0 of the RX
    frame (and the TX frame if the programmed offset
    between TX and RX is 0). In delayed mode, SFS is
    active one cycle earlier.
    The amount of skew or offset between the transmit and
    receive frames and time slots is programmable via
    board control word 2, 0x1FFC. The bit offset is up to a
    frame, i.e., up to 511 bits in 4 MHz mode. The bit offset
    skew takes place in the system PCM interface block.
    The active transmit and receive time slots are deter-
    mined by the card address. The number of time slots
    within a frame varies according to the rate of SCK. Only
    16 time slots are ever active in a frame, as shown in
    Table 3.
    The T8531 obtains its card address in board control
    word 1, 0x1FFE.
    In
    μ
    -law or A-law mode, each PCM word is only 8 bits
    long and occupies one time slot. In linear mode, the
    PCM word is 16 bits long and occupies two adjacent
    time slots. The MSB is the first bit clocked out in the
    valid time slot, and the LSB is the last bit of the follow-
    ing (invalid) time slot.
    T8531 Microprocessor Interface
    This interface between the microprocessor (or other
    external controller) and the T8531 device carries user-
    supplied program variables and control and test
    instructions to both the T8531 and the T8532 octal
    converters. The external device is the master of the
    microprocessor interface. The interface is serial and
    asynchronous, and consists of four pins (UPCK,
    UPCS, UPDI, UPDO). The data rate is determined by
    the customer’s choice of external device, but may not
    exceed 4.096 MHz. Microprocessor interface com-
    mands consist of two words, address and data.
    Address and data are 16 bits wide. The T8531 expects
    an address first. The first bit of the address word is the
    R/W flag, which tells the T8531 whether it must receive
    or send data (receive, R/W = 0; send, R/W = 1).
    Addresses less than 0x1400 refer to the DSP engine
    RAM space. If a read from the DSP engine is required,
    the microprocessor interface issues a read interrupt to
    the DSP engine. If it's a write to the DSP engine, the
    microprocessor interface shifts in the data word and
    saves it into the data register before sending a write
    interrupt to the DSP engine. Once in every 7.8
    μ
    s time
    segment, the DSP engine checks whether an interrupt
    is outstanding from the microprocessor interface block.
    If so, the DSP engine reads the address register. If it's
    a read, the DSP engine fetches the word from RAM,
    places it in the data register, and shifts it out to the
    microprocessor. If it's a write, it puts the contents of the
    data register into RAM.
    Table 3. Active Time-Slot Spacing in a PCM Bus Frame
    SCK Rate (MHz)
    2.048
    Total # of Time Slots
    32
    Card Address
    0
    1
    0
    1
    2
    3
    Valid Time Slots
    0, 2, 4, . . . 30
    1, 3, 5, . . . 31
    0, 4, 8, . . . 60
    1, 5, 9, . . . 61
    2, 6, 10, . . . 62
    3, 7, 11, . . . 63
    Invalid Time Slots
    1, 3, 5, . . . 31
    0, 2, 4, . . . 30
    1—3, 5—7, . . . 61—63
    0, 2—4, 6—8, . . . 62—63
    0—1, 3—5, 7—9, . . . 63
    0—2, 4—6, 8—10, . . . 60—62
    4.096
    64
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