XRT7250 Datasheet, PDF (267/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
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3. Interface the XRT7250, to the Terminal Equip-
ment, as illustrated in Figure 106.
NOTE: The XRT7250 Framer IC cannot support the Framer
Local Loop-back Mode of operation, while operating in
Mode 4. The user must configure the XRT7250 Framer IC
into any of the following modes prior to configuring the
Framer Local Loop-back Mode operation.
• Mode 2 - Serial/Local-Timed/Frame-Slave Mode
• Mode 3 - Serial/Local-Timed/Frame-Master Mode
• Mode 5 - Nibble-Parallel/Local-Timed/Frame-Slave
Mode
• Mode 6 - Nibble-Parallel/Local-Timed/Frame-Mas-
ter Mode.
For more detailed information on the Framer Local
Loop-back Mode, please see Section 6.0.
5.2.1.5 Mode 5 - The Nibble-Parallel/Local-
Timed/Frame-Slave Interface Mode Behavior of
the XRT7250
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 at its timing reference.
Further, the chip will internally divide the TxInClk
clock signal by a factor of 4 and will output this divid-
ed clock signal via the TxNibClk output pin. The
Transmit Terminal Equipment Input Interface block
(within the XRT7250) will use the rising edge of the
TxNibClk signal, to latch the data, residing on the Tx-
Nib[3:0] into its circuitry.
B. Nibble-Parallel Mode
The XRT7250 will accept the E3 payload data, from
the Terminal Equipment, in a parallel manner, via the
TxNib[3:0] input pins. The Transmit Terminal Equip-
ment Input Interface will latch this data into its circuit-
ry, on the rising edge of the TxNibClk output signal.
C. Delineation of outbound E3 Frames
The Transmit Section will use the TxInClk input signal
as its timing reference and will use the TxFrameRef
input signal as its Framing Reference (e.g., the Trans-
mit Section of the XRT7250 initiates frame generation
upon the rising edge of the TxFrameRef signal).
D. Sampling of payload data, from the Terminal
Equipment
In Mode 5, the XRT7250 will sample the data, at the
TxNib[3:0] input pins, on the third rising edge of the
TxInClk clock signal, following a pulse in the TxNibClk
signal (see Figure 108).
NOTE: The TxNibClk signal, from the XRT7250 operates
nominally at 8.592 MHz (e.g., 34.368 MHz divided by 4).
Interfacing the Transmit Payload Data Input Inter-
face block of the XRT7250 to the Terminal Equip-
ment for Mode 5 Operation
Figure 108 presents an illustration of the Transmit
Payload Data Input Interface block (within the
XRT7250) being interfaced to the Terminal Equip-
ment, for Mode 5 Operation.
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