XRT72L56 Datasheet, PDF (299/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
FIGURE 116. 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 # 0
TxOHEnable Pulse # 10
A bit = 1
Terminal Equipment
samples “TxOHFrame” and
“TxOHEnable” being “HIGH”
Terminal Equipment counts the number of
TxOHEnable pulses. At “pulse # 10” the Terminal
Equipment asserts the “TxOHIns” signal and places the
desired data on TxOH.
XRT72L5x samples TxOH
here.
5.2.3 The Transmit E3 HDLC Controller
The Transmit E3 HDLC Controller block can be used
to transport Message-Oriented Signaling (MOS) type
messages to the remote terminal equipment as dis-
cussed in detail below.
5.2.3.1 Message-Oriented Signaling (e.g.,
LAP-D) processing via the Transmit DS3 HDLC
Controller
The LAPD Transmitter (within the Transmit E3 HDLC
Controller Block) allows the user to transmit path
maintenance data link (PMDL) messages to the re-
mote terminal via the outbound E3 Frames. In this
case the message bits are inserted into and carried
by the “N” bit, within the outbound E3 frames. The
on-chip LAPD transmitter supports both the 76 byte
and 82 byte length message formats, and the Framer
IC allocates 88 bytes of on-chip RAM (e.g., the Trans-
mit LAPD Message buffer) to store the message to be
transmitted. The message format complies with ITU-
T Q.921 (LAP-D) protocol with different addresses
and is presented below in Figure 117 .
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