XRT7250 datasheet(281/463 Pages) EXAR

281 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

262

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 .

FIGURE 116. BEHAVIOR OF TRANSMIT OVERHEAD DATA INPUT INTERFACE SIGNALS BETWEEN THE XRT7250 AND

THE

TERMINAL EQUIPMENT (FOR METHOD 2)

TxInClk

TxOHFrame

TxOHEnable

TxOHIns

TxOH

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.

XRT7250 samples TxOH

here.

TxOHEnable Pulse # 10

A bit = 1

TxOHEnable Pulse # 0

XRT7250 Datasheet(PDF) 281 Page - Exar Corporation

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