XRT7250 datasheet(384/463 Pages) EXAR

384 / 463 page

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

365

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 XRT7250 will

transmit a Yellow Alarm to the remote terminal equip-

ment. Recall that, for E3, ITU-T G.832 applications, a

Yellow Alarm is transmitted by setting the FERF bit

(within the MA byte) to "1".

If one assumes that the connection between the Ter-

minal Equipment and the XRT7250 is as illustrated in

Figure 172 then, Figure 173 presents an illustration of

the signaling that must go on between the Terminal

Equipment and the XRT7250.

6.2.3

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.

NOTE: While executing this particular write operation, the

user should write the binary value "000xx110b" into the Tx

Controller block), please see Section 5.3.3.1.

6.2.3.1

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 either inserted into and

carried by the “NR” or the “GC” bytes, within the Out-

bound E3 frames. The on-chip LAPD transmitter sup-

ports both the 76 byte and 82 byte length message

formats, and the Framer IC allocates 88 bytes of on-

chip RAM (e.g., the Transmit LAPD Message buffer)

to store the message to be transmitted. The mes-

sage format complies with ITU-T Q.921 (LAP-D) pro-

tocol with different addresses and is presented below

in Figure 174.

FIGURE 173. 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 # 32” the Terminal

Equipment asserts the “TxOHIns” signal and places the

desired data on TxOH.

XRT7250 samples TxOH

here.

TxOHEnable Pulse # 32

MA Byte, Bit 7

TxOHEnable Pulse # 0

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