XRT72L13 Datasheet, PDF (330/370 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 109. ILLUSTRATION OF HOW TO INTERFACE THE TERMINAL EQUIPMENT TO THE “RECEIVE OVERHEAD DATA
OUTPUT INTERFACE” BLOCK (FOR METHOD 2).
DS3_OH_In
DS3_OH_Enable_In
RxOH
RxOHEnable
DS3_Clk_In
RxOutClk
Rx_Start_of_Frame
RxOHFrame
Terminal Equipment
XRT72L13 DS3 Framer IC
Method 2 Operation of the Terminal Equipment
If the Terminal Equipment intends to sample any
overhead data from the “inbound” DS3 data stream
(via the “Receive Overhead Data Output Interface),
then it is expected to do the following.
1. Sample the state of the “RxOHFrame” signal
(e.g., the “Rx_Start_of_Frame” input) on the fall-
ing edge of the “RxOutClk” clock signal; when-
ever the “RxOHEnable” output signal is also sam-
pled “high”.
2. Keep track of the number of times that the “RxO-
HEnable” signal has been sampled “high” since
the last time the “RxOHFrame” was also sampled
“high”. By doing this, the Terminal Equipment will
be able to keep track of which overhead bit is
being output via the “RxOH” output pin. Based
upon this information, the Terminal Equipment
will be able to derive some meaning from these
overhead bits.
3. Table 38 relates the number of “RxOHEnable”
output pulses (that have occurred since both the
“RxOHFrame” and the “RxOHEnable” pins were
both sampled “high”) to the DS3 overhead bit that
is being output via the “RxOH” output pin.
318