XRT7250 datasheet(186/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

167

This action will prevent the LAPD Transmitter from

generating its own one-second interrupts.

2. Enable the One-Second Interrupt

This can be done by writing a "1" into Bit 0 of the

Block Interrupt Enable 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 timing the writes to the Transmit LAPD Message

buffer to occur immediately after the occurrence of

the One-Second interrupt, the user avoids conflicting

with the one-second transmissions of the LAPD Mes-

sage, and will transmit the correct messages to the

remote LAPD Receiver.

4.2.4

The Transmit DS3 Framer Block

4.2.4.1

Brief Description of the Transmit DS3

Framer

The Transmit DS3 Framer block accepts data from

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

the DS3 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 DS3 Framer block

handles data from each of these sources is described

below.

Handling of data from the Transmit Payload Data

Input Interface

For DS3 applications, all data that is input to the

Transmit Payload Data Input Interface will be inserted

into the payload bit positions within the outbound DS3

frames.

Handling of data from the Internal Overhead Bit

Generator

By default, the Transmit DS3 Framer block will inter-

nally generate the overhead bits. However, if the Ter-

minal Equipment inserts its own values for the over-

head bits (via the Transmit Overhead Data Input Inter-

face) or, if the user enables and employs the Transmit

DS3 HDLC Controller block, then these internally

generated overhead bits will be overwritten.

Handling of data from the Transmit Overhead Da-

ta Input Interface

For DS3 applications, the Transmit DS3 Framer block

automatically generates and inserts the framing align-

ment bits (e.g., the F and M bits) into the outbound

DS3 frames. Further, the Transmit DS3 Framer block

will automatically compute and insert the P-bits into

the outbound DS3 frames. Hence, the Transmit DS3

Framer block will not accept data from the Transmit

OH Data Input Interface block for the F, M and P bits.

However, the Transmit DS3 Framer block will accept

(and insert) data from the Transmit Overhead Data In-

put Interface for the following bit-fields.

• X-bits

• FEBE bits

• FEAC bits

• DL bits

• UDL bits

• CP bits

FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)

BIT 7BIT 6BIT 5BIT 4

BIT 3BIT2BIT 1BIT 0

Local Loop-

back

DS3/E3*

Internal

LOS

Enable

RESET

Interrupt

Enable

Reset

Frame

Format

TimRefSel[1:0]

R/W

110

BLOCK INTERRUPT ENABLE REGISTER (ADDRESS = 0X04)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT2BIT 1

BIT 0

RxDS3/E3

Interrupt

Enable

Not Used

TxDS3/E3

Interrupt

Enable

One Second

Interrupt

Enable

R/W

RORO

R/W

0000

XRT7250 Datasheet(PDF) 186 Page - Exar Corporation

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