XRT72L56 Datasheet, PDF (384/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
8.592MHz clock signal at the E3_Nib_Clock_In input
pin.
The XRT72L56 will latch the Outbound E3 data
stream (from the Terminal Equipment) on the rising
edge of the TxNibClk output clock signal. The
XRT72L56 will indicate that it is processing the last
nibble, within a given E3 frame, by pulsing its TxNib-
Frame output pin "High" for one TxNibClk clock peri-
od. When the Terminal Equipment detects a pulse at
its Tx_Start_of_Frame input pin, it is expected to
transmit the first nibble, of the very next Outbound E3
frame to the XRT72L56 via the E3_Data_Out[3:0] (or
TxNib[3:0] pins).
Finally, for the Nibble-Parallel Mode operation, the
XRT72L56 will pulse the TxOHInd output pin “High”
for a total of 14 nibble periods (e.g., for the 7 over-
head bytes, within each of the E3, ITU-T G.832
frames). At the beginning of an E3 frame, the
XRT72L56 will pulse the TxOHInd output pin “High”
for 4 nibble periods. These four nibbles represent the
“FA1” and “FA2” bytes within each E3 frame.
Throughout the remainder of the E3 framing period,
the XRT72L56 will pulse the TxOHInd output pin 5
times. The width (or duration) of each of these pulses
will be two nibbles. Clearly, each of these 5 pulses
corresponds to the five remaining overhead bytes,
within the E3, ITU-T G.832 framing structure.
The behavior of the signals between the XRT72L56
and the Terminal Equipment for E3 Mode 4 Operation
is illustrated in Figure 164.
FIGURE 164. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT72L56 AND THE TERMINAL
EQUIPMENT (MODE 4 OPERATION)
Terminal Equipment Signals
RxOutClk
E3_Nib_Clock_In
E3_Data_Out[3:0]
Tx_Start_of_Frame
E3_Overhead_Ind
Payload Nibble [1059]
Overhead Nibble [0]
XRT72L5x Transmit Payload Data I/F Signals
RxOutClk
TxNibClk
TxNib[3:0]
TxNibFrame
Nibble [1059]
Overhead Nibble [0]
TxOH_Ind
Note: TxNibFrame pulses high to denote
E3 Frame Boundary.
E3 Frame Number N
E3 Frame Number N + 1
TxOH_Ind pulses high for 4 Nibble periods
How to configure the XRT72L56 into Mode 4
1. Set the NibIntf input pin "High".
2. Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to "00" as illus-
trated below.
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