XRT72L56 Datasheet, PDF (199/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
PRELIMINARY
XRT72L56
REV. P1.1.2
FIGURE 60. BEHAVIOR OF TRANSMIT OVERHEAD DATA INPUT INTERFACE SIGNALS BETWEEN THE XRT72L56 AND
THE TERMINAL EQUIPMENT (FOR METHOD 2)
TxInClk
TxOHFrame
TxOHEnable
TxOHIns
TxOH
TxOHEnable Pulse # 8
X bit = 0
X bit = 0
Terminal Equipment
samples “TxOHFrame” and
“TxOHEnable” being “HIGH”
Terminal Equipment
responds by asserting
TxOHIns and placing desired
data on TxOH.
XRT72L5x samples TxOH
here.
4.2.3 The Transmit DS3 HDLC Controller
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:
0 d5 d4 d3 d2 d1 d0 0
where '[d5, d4, d3, d2, d1, d0]' is the FEAC code
word. The rightmost bit (e.g., a 1) of the FEAC Mes-
sage, is transmitted first. Since each DS3 frame con-
tains only 1 FEAC bit, 16 DS3 Frames are required to
transmit the 16 bit FEAC Code Message.
The XRT72L56 contains the following two registers
that support FEAC Message Transmission.
• The Transmit FEAC Processor.
• The LAPD Transmitter.
This section describes how to operate the Transmit
FEAC Processor. If the Transmit DS3 Framer is oper-
ating 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:
1
1
1
1
1
1
1
1
• Tx DS3 FEAC Register (Address = 0x32)
• Tx DS3 FEAC Configuration and Status Register
(Address = 0x33)
Operating the Transmit FEAC Processor
In order to transmit a FEAC message to the remote
terminal, the user must execute the following steps.
180