XRT7250 Datasheet, PDF (263/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
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If the XRT7250 has been configured to operate in this
mode, then the XRT7250 will function as follows.
A. Local-Timed - Uses the TxInClk signal as the
Timing Reference
In this mode, the Transmit Section of the XRT7250
will use the TxInClk signal as its timing reference.
B. Serial Mode
The XRT7250 will receive the E3 payload data, in a
serial manner, via the TxSer input pin. The Transmit
Payload Data Input Interface (within the XRT7250)
will latch this data into its circuitry, on the rising edge
of the TxInClk input clock signal.
C. Delineation of outbound DS3 frames (Frame
Master Mode)
The Transmit Section of the XRT7250 will use the Tx-
InClk signal as its timing reference, and will initiate E3
frame generation, asynchronously with respect to any
externally applied signal. The XRT7250 will pulse its
TxFrame output pin "High" whenever its it processing
the very last bit-field within a given E3 frame.
D. Sampling of payload data, from the Terminal
Equipment
In Mode 3, the XRT7250 will sample the data, at the
TxSer input pin, on the rising edge of TxInClk.
Interfacing the Transmit Payload Data Input Inter-
face block of the XRT7250 to the Terminal Equip-
ment for Mode 3 Operation
Figure 104 presents an illustration of the Transmit
Payload Data Input Interface block (within the
XRT7250) being interfaced to the Terminal Equip-
ment, for Mode 3 operation.
FIGURE 104. ILLUSTRATION OF THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA
INPUT INTERFACE BLOCK OF THE XRT7250 FOR MODE 3 (SERIAL/LOCAL-TIME/FRAME-MASTER) OPERATION
34.368 MHz Clock
Source
E3_Clock_In
E3_Data_Out
Tx_Start_of_Frame
E3_Overhead_Ind
TxInClk
TxSer
TxFrame
TxOH_Ind
NibInt
Terminal Equipment
XRT7250 E3 Framer
Mode 3 Operation of the Terminal Equipment
In Figure 104, both the Terminal Equipment and the
XRT7250 are driven by an external 34.368 MHz clock
signal. This clock signal is connected to the
E3_Clock_In input of the Terminal Equipment and the
TxInClk input pin of the XRT7250.
The Terminal Equipment will serially output the pay-
load data on its E3_Data_Out output pin, upon the
rising edge of the signal at the E3_Clock_In input pin.
Similarly, the XRT7250 will latch the data, residing on
the TxSer input pin, on the rising edge of TxInClk.
The XRT7250 will pulse the TxFrame output pin
"High" for one bit-period, coincident while it is pro-
cessing the last bit-field within a given outbound E3
frame. The Terminal Equipment is expected to moni-
tor the TxFrame signal (from the XRT7250) and to
place the first bit, within the very next outbound E3
frame on the TxSer input pin.
NOTE: In this case, the XRT7250 dictates exactly when the
very next E3 frame will be generated. The Terminal Equip-
ment is expected to respond appropriately by providing the
XRT7250 with the first bit of the new E3 frame, upon
demand. Hence, in this mode, the XRT7250 is referred to
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