XRT72L13 Datasheet, PDF (251/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
turn, the "TxFrameRef" input pin of the XRT72L13),
"high" for one-bit period, coincident with the first bit of
a new DS3 frame. Once the XRT72L13 detects the
rising edge of the input at its "TxFrameRef" input pin;
it will begin generation of a new DS3 frame.
NOTES:
1. In this case, the Terminal Equipment is controlling
the "start" of Frame Generation, and is therefore
referred to as the "Frame Master". Conversely,
since the XRT72L13 does not control the genera-
tion of a new DS3 frame, but is rather driven by the
"Terminal Equipment". Hence, the XRT72L13 is
referred to as the "Frame Slave".
2. If the user opts to configure the XRT72L13 to oper-
ate in Mode 2, it is imperative that the
"Tx_Start_of_Frame" (or "TxFrameRef") signal is
synchronized to the "TxInClk" input clock signal.
Finally, the XRT72L13 will pulse its "TxOH_Ind" out-
put pin, one bit-period prior to it processing a given
"overhead" bit, within the "outbound" DS3 frame.
Since the "TxOH_Ind" output pin (of the XRT72L13)
is electrically connected to the "DS3_Overhead_Ind";
whenever the XRT72L13 pulses the "TxOH_Ind" out-
put pin "high", it will also be driving the
"DS3_Overhead_Ind" input pin (of the Terminal
Equipment) "high". Whenever the Terminal Equip-
ment detects this pin toggling "high", it should delay
transmission of the very next "DS3 frame" payload bit
by one clock cycle.
The behavior of the signals between the XRT72L13
and the Terminal Equipment for DS3 Mode 2 Opera-
tion is illustrated in Figure 66 .
FIGURE 66. BEHAVIOR OF THE "TERMINAL INTERFACE" SIGNALS BETWEEN THE XRT72L13 AND THE TERMINAL
EQUIPMENT (MODE 2 OPERATION)
Terminal Equipment Signals
DS3_Clock_In
DS3_Data_Out
Tx_Start_of_Frame
DS3_Overhead_Ind
Payload[4702] Payload[4703]
X-Bit
Payload[1]
XRT72L13 Transmit Payload Data I/F Signals
TxInClk
TxSer
Payload[4702] Payload[4703]
TxFrameRef
TxOH_Ind
X-Bit
Payload[1]
DS3 Frame Number N
DS3 Frame Number N + 1
Note: TxOH_Ind pulses high to
Note: X-Bit will not be processed by the
Transmit Payload Data Input Interface.
denote Overhead Data
(e.g., the X-bit).
Note: TxFrame pulses high to denote
DS3 Frame Boundary.
How to configure the XRT72L13 to operate in this
mode.
1. Set the "NibIntf" input pin "low".
2. Set the "TimRefSel[1:0] bit-fields (within the
"Framer Operating Mode Register") to "01" as
depicted below.
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