XRT7250 datasheet(121/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

102

Bit 3 - Auto Retransmit

This Read/Write bit-field allows the user to configure

the LAPD Transmitter to either transmit the LAPD

Message frame only once, or repeatedly at one-sec-

ond intervals.

Writing a "0" to this bit-field configures the LAPD

Transmitter to transmit the LAPD Message frame

once. Afterwards, the LAPD Transmitter will halt

transmission, until it has commanded to transmit an-

other LAPD Message frame.

Writing a "1" to this bit-field configures the LAPD

Transmitter to transmit the LAPD Message frame re-

peatedly at One-Second intervals. In this configura-

tion, the LAPD Transmitter will repeat its transmission

of the LAPD Message frame until it has been dis-

abled.

Bit 1 - TxLAPD Message Length Select

This Read/Write bit-field permits the user to select

the length of the outbound LAPD Message frame.

Setting this bit-field to "0" configures the outbound

LAPD Message frame to be 76 bytes in length. Set-

ting this bit-field to "1" configures the outbound LAPD

Message frame to be 82 bytes in length.

Bit 0 - TxLAPD Enable

This Read/Write bit-field allows the user to enable or

disable the LAPD Transmitter. The LAPD Transmitter

must be enabled before it can be commanded to

transmit a LAPD Message frame (containing a PMDL

message) via the outbound DS3 frames, to the Far-

End Terminal.

Writing a "0" disables the LAPD Transmitter (default

condition). Writing a "1" enables the LAPD Transmit-

ter.

NOTE: For information on the LAPD Transmitter, please see

Section 4.2.3.

2.3.7.3

Transmit E3 LAPD Status and Interrupt

Bit 3 - TxDL Start

This Read/Write bit-field allows the user to command

the LAPD Transmitter to do the following.

• Scan through the PMDL Message, within the Trans-

mit LAPD Message buffer, and search for a string of

five (5) consecutive "1’s". The LAPD Transmitter

will then insert (or stuff) a "0" into the PMDL Mes-

sage data, immediately following any string of 5

consecutive "1’s".

• Read in this stuffed PMDL Message from the Trans-

mit LAPD Message buffer, and encapsulate it into a

LAPD Message frame.

• Fragment the resulting LAPD Message frame into

octets.

• Insert these octets into either the GC byte-field or

the NR byte-field (depending upon the user's selec-

tion) in each outbound E3 frame.

A "0" to "1" transition, in this bit-field commands the

LAPD Transmitter to initiate the above-mentioned

procedure.

NOTE: Once the user has commanded the LAPD Transmit-

ter to start transmission, the LAPD Transmitter will repeat

the above-mentioned process once each second and will

TXE3 LAPD CONFIGURATION REGISTER (ADDRESS = 0X33)

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

Not Used

Auto Retrans-

mit

Not Used

TxLAPD

Msg Length

TxLAPD

Enable

R/W

001

000

TXE3 LAPD STATUS AND INTERRUPT REGISTER (ADDRESS = 0X34)

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

Not Used

TXDL Start

TXDL Busy

TxLAPD

Interrupt

Enable

TxLAPD

Interrupt

Status

R/W

RUR

000

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