XRT74L73 Datasheet, PDF (313/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
TABLE 67: THE RELATIONSHIP BETWEEN THE NUMBER OF TXOHENABLE PULSES (SINCE THE LAST OCCURRENCE OF
THE TXOHFRAME PULSE) TO THE E3 OVERHEAD BIT, THAT IS BEING PROCESSED BY THE XRT74L73
NUMBER OF TXOHENABLE PULSES
0 (Clock edge is coincident with TxO-
HFrame being detected "High”)
1
2
3
4
5
6
7
8
9
10
11
THE OVERHEAD BIT EXPECTED BY THE CAN THIS OVERHEAD BIT BE ACCEPTED BY
XRT74L73
THE XRT74L73?
FAS Signal - Bit 9
Yes
FAS Signal - Bit 8
Yes
FAS Signal - Bit 7
Yes
FAS Signal - Bit 6
Yes
FAS Signal - Bit 5
Yes
FAS Signal - Bit 4
Yes
FAS Signal - Bit 3
Yes
FAS Signal - Bit 2
Yes
FAS Signal - Bit 1
Yes
FAS Signal - Bit 0
Yes
A Bit
Yes
N Bit
Yes
3. After the Terminal Equipment has waited through
the appropriate number of pulses via the TxO-
HEnable pin, it should then assert the TxOHIns
input signal. Concurrently, the Terminal Equip-
ment should also place the appropriate value (of
the inserted overhead bit) onto the TxOH signal.
4. The Terminal Equipment should hold both the
TxOHIns input pin "High" and the value of the
TxOH signal stable, until the next TxOHEnable
pulse is detected.
Case Study: The Terminal Equipment intends to
insert the appropriate overhead bits into the
Transmit Overhead Data Input Interface (using
Method 2) in order to transmit a Yellow Alarm to
the remote terminal equipment.
In this case, the Terminal Equipment intends to insert
the appropriate overhead bits, into the Transmit Over-
head Data Input Interface such that the XRT74L73
will transmit a Yellow Alarm to the remote terminal
equipment. Recall that, for E3, ITU-T G.751 applica-
tions, a Yellow Alarm is transmitted by setting the “A”
bit to “1".
If one assumes that the connection between the Ter-
minal Equipment and the XRT74L73 is as illustrated
in Figure 122 then, Figure 123 presents an illustra-
tion of the signaling that must go on between the Ter-
minal Equipment and the XRT74L73.
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