XRT7250 Datasheet, PDF (276/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
TABLE 49: THE RELATIONSHIP BETWEEN THE NUMBER OF RISING CLOCK EDGES IN TXOHCLK, (SINCE TXOHFRAME
WAS LAST SAMPLED "HIGH") TO THE E3 OVERHEAD BIT, THAT IS BEING PROCESSED
NUMBER OF RISING CLOCK EDGES IN
TXOHCLK
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
XRT7250
THE XRT7250?
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 the
appropriate number of clock edges (from the
TxOHFrame signal being sampled "High"), it
should assert the TxOHIns input signal. Concur-
rently, 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 rising edge of
TxOHClk is detected.
Case Study: The Terminal Equipment intends to
insert the appropriate overhead bits into the
Transmit Overhead Data Input Interface (using
Method 1) in order to transmit a Yellow Alarm to
the remote terminal equipment.
In this example, the Terminal Equipment intends to in-
sert the appropriate overhead bits, into the Transmit
Overhead Data Input Interface, such that the
XRT7250 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 Ter-
minal Equipment and the XRT7250 are as illustrated
in Figure 113 then Figure 114 presents an illustration
of the signaling that must go on between the Terminal
Equipment and the XRT7250.
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