參數(shù)資料
型號: XRT75R12IB
廠商: EXAR CORP
元件分類: 數(shù)字傳輸電路
英文描述: TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR
中文描述: DATACOM, PCM TRANSCEIVER, PBGA420
封裝: 35 X 35 MM, TBGA-420
文件頁數(shù): 22/89頁
文件大小: 457K
代理商: XRT75R12IB
XRT75R12
REV. P1.0.2
PRELIMINARY
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR
19
2.0
CLOCK SYNTHESIZER
The LIU uses a flexible user interface for accepting clock references to generate the internal master clocks
used to drive the LIU. The reference clock used to supply the microprocessor timing is generated from the DS-
3 or SFM clock input. Therefore, if the chip is configured for STS-1 only or E3 only, then the DS-3 input pin
must be connected to the STS-1 pin or E3 pin respectively. In DS-3 mode or when SFM is used, the STS-1
and E3 input pins can be left unconnected. If SFM is enabled by pulling the SFM_EN pin "High", 12.288MHz is
the only clock reference necessary to generate DS-3, E3, or STS-1 line rates and the microprocessor timing.
A simplified block diagram of the clock synthesizer is shown in Figure 3
2.1
Network cards that are designed to support multiple line rates which are not configured for single frequency
mode should ensure that a clock is applied to the DS3Clk input pin. For example: If the network card being
supplied to an ISP requires E3 only, the DS-3 input clock reference is still necessary to provide read and write
access to the internal microprocessor. Therefore, the E3 mode requires two input clock references. If
however, multiple line rates will not be supported, i.e. E3 only, then the DS3Clk input pin may be hard wire
connected to the E3Clk input pin.
Clock Distribution
F
IGURE
4. C
LOCK
D
ISTRIBUTION
C
ONGIFURED
IN
E3 M
ODE
W
ITHOUT
U
SING
SFM
N
OTE
:
For one input clock reference, the single frequency mode should be used.
F
IGURE
3. S
IMPLIFIED
B
LOCK
D
IAGRAM
OF
THE
I
NPUT
C
LOCK
C
IRCUITRY
D
RIVING
THE
M
ICROPROCESSOR
Clock Synthesizer
μ
Processor
LOL_n
DS3Clk
SFM_EN
STS-1Clk/12M
E3Clk
CLKOUT_n
0
1
Clock Synthesizer
μ
Processor
LOL_n
DS3Clk
E3Clk
CLKOUT_n
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