
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
211
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 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 XRT74L73 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 XRT74L73.
4.2.3
The Transmit DS3 HDLC Controller block can be
used to transport either Bit-Oriented Signaling (BOS)
or Message-Oriented Signaling (MOS) type messag-
es or both types of messages to the remote terminal
equipment. Both BOS and MOS types of HDLC mes-
sage processing are discussed in detail below.
4.2.3.1
Bit-Oriented Signaling (or FEAC Mes-
sage) processing via the Transmit DS3 HDLC
Controller.
The Transmit DS3 HDLC Controller block consists of
two major blocks:
The Transmit DS3 HDLC Controller
The Transmit FEAC Processor.
The LAPD Transmitter.
This section describes how to operate the Transmit
FEAC Processor. If the Transmit DS3 Framer is op-
erating in the C-bit Parity Framing Format then the
FEAC (Far-End Alarm & Control) bit-field of the DS3
Frame can be used to transmit the FEAC messages
(See Figure 42). The FEAC code word is a 6-bit val-
ue which is encapsulated by 10 framing bits, forming
a 16-bit FEAC message of the form:
F
IGURE
67. B
EHAVIOR
OF
T
RANSMIT
O
VERHEAD
D
ATA
I
NPUT
I
NTERFACE
SIGNALS
BETWEEN
THE
XRT74L73
AND
THE
T
ERMINAL
E
QUIPMENT
(
FOR
M
ETHOD
2)
TxInClk
TxOHFrame
TxOHEnable
TxOHIns
TxOH
Terminal Equipment
samples “TxOHFrame” and
“TxOHEnable” being “HIGH”
Terminal Equipment
responds by asserting
TxOHIns and placing desired
data on TxOH.
XRT72L5x samples TxOH
here.
TxOHEnable Pulse # 8
X bit = 0
X bit = 0