XRT7250 datasheet(102/463 Pages) EXAR

102 / 463 page

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

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

disable the Received LAPD Message frame interrupt.

Setting this bit-field to "1" enables this interrupt. Set-

ting this bit-field to "0" disables this interrupt.

NOTE: For more information on this interrupt, please see

Section 4.3.6.1.9.

Bit 0 - RxLAPD (Received LAPD Message) Inter-

rupt Status

This Reset-upon-Read bit-field will be set to "1" if the

Receipt of New LAPD Message frame interrupt has

occurred since the last read of this register.

The Receive E3 Framer will generate this Receipt of

New LAPD Message frame interrupt when the LAPD

Receiver has received a complete LAPD Message

frame from the Remote LAPD Transmitter.

NOTE: Please see section 4.3.6.1.9 for a more detailed dis-

cussion of this interrupt.

2.3.4.8

Receive E3 LAPD Status Register (E3,

ITU-T G.751)

Bit 6 - RxAbort

This Read-Only bit-field indicates whether or not the

LAPD Receiver is currently detecting an abort se-

quence (e.g., a string of 7 consecutive "1’s").

This bit-field is set to "1" if the LAPD Receiver is cur-

rently detecting an abort sequence in the incoming

LAPD Channel. Conversely, this bit-field is set to "0"

if the LAPD Receiver has not detected an abort se-

quence, since the last read of this register.

Bit 5, 4 - RxLAPD Type[1:0]

These two Read-Only bit-fields combine to indicate

the type and size of LAPD Message frame that has

been received by the LAPD Receiver. The following

table relates the contents of these bit-fields to the

LAPD Message type/size.

Bit 3 - RxCR Type

This Read-Only bit-field indicates the state of the C/R

bit-field, within octet # 2 of the most recently received

LAPD Message frame.

Bit 2 - RxFCS Error

This Read-Only bit-field indicates whether or not the

LAPD Receiver has detected an FCS (Frame Check

Sequence) error, in the most recently received LAPD

Message frame. This bit-field is set to "0" if the LAPD

Receiver does not detect an FCS error in this LAPD

Message frame. Conversely, this bit-field is set to "1"

if the LAPD Receiver does detect an FCS error in this

LAPD Message frame.

NOTE: For a more detailed discussion on the LAPD

Receiver's handling of the FCS bytes, please see Section

4.3.3.

Bit 1 - EndOfMessage

The LAPD Receiver will assert this read-only bit-field,

when it has received a complete LAPD Message

frame. This bit-field, along with the Receipt of New

LAPD Message frame interrupt, serves to inform the

local µP that the Receive LAPD Message buffer con-

tains a new PMDL message that needs to be read

and processed.

This bit-field is cleared (to "0") upon reading this reg-

ister.

RXE3 LAPD STATUS REGISTER (ADDRESS = 0X19)

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

Not Used

RxAbort

RxLAPDType[1:0]

RxCR Type

RxFCS Error

End of

Message

Flag Present

0000

000

RXLAPDTYPE[1:0]

LAPD MESSAGE FRAME TYPE

PMDL MESSAGE SIZE (INFORMATION

SECTION)

Test Signal Identification Type

76 Bytes

Idle Signal Identification Type

76 Bytes

CL Path Identification Type

76 Bytes

ITU-T Path Identification Type

82 Bytes

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