XRT72L56 Datasheet, PDF (385/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Local Loopback DS3/E3* Internal LOS
Enable
RESET
Interrupt Frame Format
Enable Reset
TimRefSel[1:0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
1
0
1
0
0
0
3. Interface the XRT72L56, 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
XRT72L56
If the XRT72L56 has been configured to operate in
this mode, then the XRT72L56 will function as fol-
lows:
A. Local Timing - Uses the TxInClk signal as the
Timing Reference
In this mode, the Transmit Section of the XRT72L56
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 XRT72L56) 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 XRT72L56 will accept the DS3 payload data,
from the Terminal Equipment, in a parallel manner,
via the TxNib[3:0] input pins. The Transmit Terminal
Equipment Input Interface will latch this data into its
circuitry, 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 XRT72L56 initiates frame genera-
tion upon the rising edge of the TxFrameRef signal).
D. Sampling of payload data, from the Terminal
Equipment
In Mode 5, the XRT72L56 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 XRT72L56 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 XRT72L56 to the Terminal Equip-
ment for Mode 5 Operation
Figure 165 presents an illustration of the Transmit
Payload Data Input Interface block (within the
XRT72L56) being interfaced to the Terminal Equip-
ment, for Mode 5 Operation.
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