XRT7250 datasheet(111/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

2.3.6.3

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

insert flag sequence octets into the outbound LAPD chan-

nel, during the idle periods between transmissions.

Bit 2 - TxDL Busy

This Read-Only bit-field allows the user to poll or

monitor the status of the LAPD Transmitter to see if it

has completed its transmission of the LAPD Message

frame. The LAPD Transmitter will set this bit-field to

"1", while it is in the process of transmitting the LAPD

Message frame. However, the LAPD Transmitter will

clear this bit-field to "0" once it has completed its

transmission of the LAPD Message frame.

Bit 1 - TxLAPD Interrupt Enable

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

disable the LAPD Message frame Transmission Com-

plete interrupt.

Writing a "0" to this bit-field disables this interrupt.

Writing a "1" to this bit-field enables this interrupt.

Bit 0 - TxLAPD Interrupt Status

This Reset-upon-Read bit-field allows the user to de-

termine if the LAPD Message Frame Transmission

Complete interrupt has occurred since the last read of

this register. If this bit-field contains a "1" then the

LAPD Message Frame Transmission Complete inter-

rupt has occurred since the last read of this register.

Conversely, if this bit-field contains a "0" then it has

not.

2.3.6.4

Transmit E3 GC Byte Register (E3, ITU-

T G.832)

This Read/Write byte-field allows the user to specify

the contents of the GC byte-field in each outbound E3

frame.

NOTE: The contents of this register is ignored, if the LAPD

Transmitter is enabled and has been configured to insert

the comprising octets of an outbound LAPD Message

frame into the GC byte-field of each outbound E3 frame

(e.g., if DLinNR = "0").

2.3.6.5

Transmit E3 MA Byte Register (E3, ITU-

T G.832)

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

TXE3 GC BYTE REGISTER (ADDRESS = 0X35)

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

TxGC[7:0]

R/W

000

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