XRT7250 datasheet(254/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

235

condition), then it will inform the Remote Terminal

Equipment of this fact by commanding the Local

Transmit E3 Framer block to set the “A” bit-field, with-

in the next outbound E3 frame, to “1”. The Local

Transmit E3 Framer block will continue to set the “A”

bit-field (within the subsequent outbound E3 frames)

to “1” until the Receive E3 Framer block no longer ex-

periences problems in receiving the E3 frame data. If

the Remote Terminal Equipment receives a certain

number of consecutive E3 frames, with the “A” bit-

field set to “1”, then the Remote Terminal Equipment

will interpret this signaling as an indication of a Far-

End Receive Failure (e.g., a problem with the Local

Terminal Equipment).

Conversely, if the Receive E3 Framer block (at a Lo-

cal Terminal Equipment) is not experiencing any

problems receiving E3 frame data from a Remote Ter-

minal Equipment, then it will also inform the Remote

Terminal Equipment of this fact by commanding the

Local Transmit E3 Framer block to set the “A” bit-field

within an outbound E3 frame (which is destined for

the Remote Terminal) to “0”. The Remote Terminal

Equipment will interpret this form of signaling as an

indication of a normal operation.

A detailed discussion into the practical use of the A

bit-field is presented in Section 4.2.2.

5.1.1.2

The “N” Bit

The “N” bit is typically used to transport PMDL (Path

Maintenance Data Link) information, from one termi-

nal to the next. However, the “N” bit-field can also be

used to transport a proprietary data link, if configured

according.

A detailed discussion into the practical use of the N-

bit field is presented in Section 4.2.2.

5.2

THE TRANSMIT SECTION OF THE XRT7250 (E3,

ITU-T G.751 MODE OPERATION)

When the XRT7250 has been configured to operate

in the E3, ITU-T G.751 Mode, the Transmit Section of

the XRT7250 consists of the following functional

blocks.

• Transmit Payload Data Input Interface block

• Transmit Overhead Data Input Interface block

• Transmit E3 Framer block

• Transmit HDLC Controller block

• Transmit LIU Interface block

Figure 98 presents a simple illustration of the Trans-

mit Section of the XRT7250 Framer IC.

Each of these functional blocks will be discussed in

detail in this document.

5.2.1

The Transmit Payload Data Input Interface

Block

Figure 99 presents a simple illustration of the Trans-

mit Payload Data Input Interface block.

FIGURE 98. A SIMPLE ILLUSTRATION OF THE XRT7250 TRANSMIT SECTION WHEN IT HAS BEEN CONFIGURED TO

OPERATE IN THE

E3 MODE

Transmit

Payload Data

Input

Interface Block

Transmit DS3/E3

Framer Block

Transmit LIU

Interface

Block

TxSer

TxNib[3:0]

TxInClk

TxPOS

TxNEG

TxLineClk

Transmit Overhead

Input

Interface Block

TxOHClk

TxOHIns

TxOHInd

TxOH

TxOHEnable

TxOHFrame

TxNibClk

TxFrame

Tx E3 HDLC

Controller/Buffer

Tx E3 HDLC

Controller/Buffer

From Microprocessor

Interface Block

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