XRT72L54 Datasheet, PDF (284/484 Pages) Exar Corporation – FOUR CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L54
FOUR CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
Mode 5 Operation of the Terminal Equipment
In Figure 108 both the Terminal Equipment and the
XRT72L54 will be driven by an external 8.592MHz
clock signal. The Terminal Equipment will receive the
8.592MHz clock signal via the E3_Nib_Clock_In input
pin. The XRT72L54 will output the 8.592MHz clock
signal via the TxNibClk output pin.
The Terminal Equipment will serially output the data
on the E3_Data_Out[3:0] pins, upon the rising edge
of the signal at the E3_Clock_In input pin.
NOTE: The E3_Data_Out[3:0] output pins of the Terminal
Equipment is electrically connected to the TxNib[3:0] input
pins.
The XRT72L54 will latch the data, residing on the Tx-
Nib[3:0] input pins, on the rising edge of the TxNibClk
signal.
In this case, the Terminal Equipment has the respon-
sibility of providing the framing reference signal by
pulsing the Tx_Start_of_Frame output pin (and in
turn, the TxFrameRef input pin of the XRT72L54)
"High" for one bit-period, coincident with the first bit of
a new E3 frame. Once the XRT72L54 detects the ris-
ing edge of the input at its TxFrameRef input pin, it
will begin generation of a new E3 frame.
Finally, the XRT72L54 will always internally generate
the Overhead bits, when it is operating in both the E3
and Nibble-parallel modes. The XRT72L54 will pull
the TxOHInd input pin "Low".
The behavior of the signals between the XRT72L54
and the Terminal Equipment for E3 Mode 5 Operation
is illustrated in Figure 109.
FIGURE 109. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT72L54 AND THE TERMINAL
EQUIPMENT (E3, MODE 5 OPERATION)
Terminal Equipment Signals
TxInClk
E3_Nib_Clock_In
E3_Data_Out[3:0]
Tx_Start_of_Frame
E3_Overhead_Ind
Payload Nibble [380]
Overhead Nibble [0]
XRT72L5x Transmit Payload Data I/F Signals
TxInClk
TxNibClk
TxNib[3:0]
TxFrameRef
Nibble [380]
Overhead Nibble [0]
TxOH_Ind
Note: Terminal Equipment pulses
“TxFrameRef” in order to denote
the E3 Frame Boundary.
E3 Frame Number N
E3 Frame Number N + 1
TxOH_Ind pulses high for 3 Nibble periods
How to configure the XRT72L54 into Mode 5
1. Set the NibIntf input pin "High".
2. Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to "01" as illus-
trated below.
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