XRT7250 datasheet(392/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

REV. 1.1.1

373

ment. In order to avoid this problem, while writing the

new message into the Transmit LAPD Message buff-

er, the user should do the following.

1. Configure the Framer to automatically reset acti-

vated interrupts.

The user can do this by writing a “1” into Bit 3 within

the Framer Operating Mode register (Address =

0x00), as depicted below.

This action will prevent the LAPD Transmitter from

generating its own One-Second interrupt (following

each transmission of the LAPD Message frame).

2. Enable the One-Second Interrupt

This can be done by writing a “1” into Bit 0 (One-Sec-

ond Interrupt Enable) within the Block Interrupt En-

able Register, as depicted below.

3. Write the new message into the Transmit LAPD

Message buffer immediately after the occurrence

of the One-Second Interrupt

By synchronizing the writes to the Transmit LAPD

Message buffer to occur immediately after the occur-

rence of the One-Second Interrupt, the user avoids

conflicting with the One-Second transmission of the

LAPD Message frame, and will transmit the correct

(uncorrupted) PMDL Message to the Remote LAPD

Receiver.

6.2.4

The Transmit E3 Framer Block

6.2.4.1

Brief Description of the Transmit E3

Framer

The Transmit E3 Framer block accepts data from any

of the following three sources, and uses it to form the

E3 data stream.

• The Transmit Payload Data Input block

• The Transmit Overhead Data Input block

• The Transmit HDLC Controller block

• The Internal Overhead Data Generator

The manner in how the Transmit E3 Framer block

handles data from each of these sources is described

below.

Handling of data from the Transmit Payload Data

Input Interface

For E3 applications, all data that is input to the Trans-

mit Payload Data Input Interface will be inserted into

the payload bit positions within the Outbound E3

frames.

Handling of data from the Internal Overhead Bit

Generator

By default, the Transmit E3 Framer block will internal-

ly generate the overhead bytes. However, if the Ter-

minal Equipment inserts its own values for the over-

head bits or bytes (via the Transmit Overhead Data

Input Interface) or, if the user enables and employs

the Transmit E3 HDLC Controller block, then these in-

ternally generated overhead bytes will be overwritten.

Handling of data from the Transmit Overhead Da-

ta Input Interface

FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0

Local Loopback

DS3/E3*

Internal

LOS

Enable

RESET

Interrupt

Enable Reset

Frame Format

TimRefSel[1:0]

R/W

BLOCK INTERRUPT ENABLE REGISTER (ADDRESS = 0X04)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0

RxDS3/E3

Interrupt

Enable

Not Used

TxDS3/E3

Interrupt

Enable

One-Second

Interrupt

Enable

R/W

RORO

R/W

0000

000

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