XRT72L53 Datasheet, PDF (274/467 Pages) Exar Corporation – THREE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L53
THREE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.8
FIGURE 113. ILLUSTRATION OF THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT OVERHEAD DATA
INPUT INTERFACE (METHOD 1)
34.368 MHz Clock Source
E3_OH_Clock_In
E3_OH_Out]
Tx_Start_of_Frame
Insert_OH
TxInClk
TxOHClk
TxOH
TxOHFrame
TxOHIns
RxLineClk
34.368 MHz
Clock Source
Terminal Equipment
XRT72L5x E3 Framer
Method 1 Operation of the Terminal Equipment
If the Terminal Equipment intends to insert any over-
head data into the outbound E3 data stream, (via the
Transmit Overhead Data Input Interface), then it is ex-
pected 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
E3_OH_Clock_In signal).
2. To keep track of the number of rising clock edges
that have occurred, via the TxOHClk (e.g., the
E3_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 processed by
the Transmit Overhead Data Input Interface block
at any given time. When the Terminal 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 out-
bound E3 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 XRT72L53).
Table 50 relates the number of rising clock edges (in
the TxOHClk signal, since TxOHFrame was sampled
"High") to the E3 Overhead Bit, that is being pro-
cessed.
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