XRT74L74 Datasheet, PDF (224/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
REV. P1.1.1
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
TABLE 39: THE RELATIONSHIP BETWEEN THE NUMBER OF TXOHENABLE PULSES (SINCE THE LAST OCCURRENCE OF
THE TXOHFRAME PULSE) TO THE DS3 OVERHEAD BIT, THAT IS BEING PROCESSED BY THE XRT74L74
NUMBER OF TXOHENABLE PULSES
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
THE OVERHEAD BIT EXPECTED BY THE CAN THIS OVERHEAD BIT BE ACCEPTED BY
XRT74L74
THE XRT74L74?
DL
Yes
F1
No
M1
No
F1
No
UDL
Yes
FO
No
UDL
Yes
FO
No
UDL
Yes
F1
No
M0
No
F1
No
UDL
Yes
F0
No
UDL
Yes
F0
No
UDL
Yes
F1
No
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 XRT74L74
will transmit a Yellow Alarm to the remote terminal
equipment. Recall that, for DS3 applications, a Yel-
low Alarm is transmitted by setting all of the X bits to
0.
If one assumes that the connection between the Ter-
minal Equipment and the XRT74L74 is as illustrated
in Figure 66 then, Figure 67 presents an illustration of
the signaling that must go on between the Terminal
Equipment and the XRT74L74.
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