XRT72L13 Datasheet, PDF (266/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
áç
PRELIMINARY
FIGURE 76. ILLUSTRATION OF THE "TERMINAL EQUIPMENT" BEING INTERFACED TO THE "TRANSMIT OVERHEAD
DATA INPUT INTERFACE" (METHOD 1)
DS3_OH_Clock_In
DS3_OH_Out]
Tx_Start_of_Frame
Insert_OH
Terminal Equipment
44.736 MHz Clock Source
TxInClk
TxOHClk
TxOH
TxOHFrame
TxOHIns
RxLineClk
44.736 MHz
Clock Source
XRT72L13 DS3 Framer
Method 1 Operation of the Terminal Equipment
If the Terminal Equipment intends to insert any over-
head data into the "outbound" DS3 data stream, (via
the Transmit Overhead Data Input Interface), then it is
expected to do the following.
1. To sample the state of the "TxOHFrame" signal
(e.g., the "Tx_Start_of_Frame" input signal) on
the rising edge of the "TxOHClk" (e.g., the
"DS3_OH_Clock_In" signal).
2. To keep track of the number of rising clock edges
that have occurred, via the "TxOHClk" (e.g., the
"DS3_OH_Clock_In" signal) since the last time
the "TxOHFrame" signal was sampled "high". By
doing this the Terminal Equipment will be able to
keep track of which overhead bit is being pro-
cessed by the “Transmit Overhead Data Input
Interface” block at any given time. When the Ter-
minal Equipment “knows” which overhead bit is
being processed, at a given “TxOHClk” period, it
will know when to insert a desired overhead bit
value into the “outbound” DS3 data stream. From
this, the Terminal Equipment will know when it
should assert the “TxOHIns” input pin and place
the appropriate value on the “TxOH” input pin (of
the XRT72L13).
Table 15 relates the number of rising clock edges (in
the "TxOHClk" signal, since "TxOHFrame" was sam-
pled "high") to the DS3 Overhead Bit, that is being
processed.
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