XRT72L56 Datasheet, PDF (293/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

áç
PRELIMINARY
XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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 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 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 XRT72L56).
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.
274