XRT7250 Datasheet, PDF (367/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
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FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
R/W
R/W
R/W
R/W
0
0
1
0
3. Interface the XRT7250, to the Terminal Equip-
ment, as illustrated in Figure 163.
6.2.1.5 Mode 5 - The Nibble-Parallel/Local-
Time/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 Timing - 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 DS3 payload data, from
the Terminal Equipment, in a parallel manner, via the
TxNib[3:0] input pins. The Transmit Terminal Equip-
BIT 3
BIT2
BIT 1
BIT 0
R/W
R/W
R/W
R/W
1
0
0
0
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 166).
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 165 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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