XRT72L50 Datasheet, PDF (280/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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TABLE 48: 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 XRT72L50
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
XRT72L50
THE XRT72L50?
FAS Signal - Bit 9
No
FAS Signal - Bit 8
No
FAS Signal - Bit 7
No
FAS Signal - Bit 6
No
FAS Signal - Bit 5
No
FAS Signal - Bit 4
No
FAS Signal - Bit 3
No
FAS Signal - Bit 2
No
FAS Signal - Bit 1
No
FAS Signal - Bit 0
No
A Bit
Yes
N Bit
Yes
3. After the Terminal Equipment has waited through the appropriate number of pulses via the TxOHEnable
pin, it should then assert the TxOHIns input signal. Concurrently, the Terminal Equipment 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
Overhead Data Input Interface such that the XRT72L50 will transmit a Yellow Alarm to the remote terminal
equipment. Recall that, for E3, ITU-T G.751 applications, a Yellow Alarm is transmitted by setting the A bit to
“1".
If one assumes that the connection between the Terminal Equipment and the XRT72L50 is as illustrated in
Figure 103 then, Figure 104 presents an illustration of the signaling that must go on between the Terminal
Equipment and the XRT72L50.
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