XRT74L73 Datasheet, PDF (364/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
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 falling edge
of the RxOutClk clock signal, whenever the RxO-
HEnable output signal is also sampled "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 82 relates the number of RxOHEnable
output pulses (that have occurred since both the
RxOHFrame and the RxOHEnable pins were
both sampled "High”) to the E3 overhead bit that
is being output via the RxOH output pin.
TABLE 82: THE RELATIONSHIP BETWEEN THE NUMBER OF RXOHENABLE OUTPUT PULSES (SINCE RXOHFRAME
WAS LAST SAMPLED "HIGH") TO THE E3 OVERHEAD BIT, THAT IS BEING OUTPUT VIA THE RXOH OUTPUT PIN
NUMBER OF RXOHENABLE OUTPUT PULSES
0 (Clock edge is coincident with RxOHFrame being detected "High”)
1
2
3
4
5
6
7
8
9
10
11
THE OVERHEAD BIT BEING OUTPUT BY THE
XRT74L73
FAS Pattern - Bit 9
FAS Pattern - Bit 8
FAS Pattern - Bit 7
FAS Pattern - Bit 6
FAS Pattern - Bit 5
FAS Pattern - Bit 4
FAS Pattern - Bit 3
FAS Pattern - Bit 2
FAS Pattern - Bit 1
FAS Pattern - Bit 0
A Bit
N Bit
Figure 155 presents the typical behavior of the Re-
ceive Overhead Data Output Interface block, when
Method 2 is being used to sample the incoming E3
overhead bits.
365