XRT7250 datasheet(92/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

NOTE: For a more detailed discussion on the LAPD

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

5.3.3.

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.

Bit 0 - Flag Present

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

when it is currently detecting the Flag Sequence octet

(7Eh) in the incoming LAPD channel (e.g., either the

GC or the NR byte-field, within each E3 frame). The

LAPD Receiver will negate this bit-field when it is no

longer receiving the Flag Sequence octet in the in-

coming LAPD channel.

2.3.3.9

Receive E3 NR Byte Register (E3, ITU-T

G.832)

This Read-Only register contains the value of the NR

byte, within the most recently received E3 frame.

Please see Section 5.3.3 for a more detailed discus-

sion on this register.

2.3.3.10 Receive E3 GC Byte Register (E3, ITU-

T G.832)

This Read-Only register contains the value of the GC

byte, residing in the most recently received E3 frame.

Please see Section 5.3.3 for a more detailed discus-

sion on this register.

2.3.3.11 Receive E3 TTB-0 Register (E3, ITU-T

G.832)

This Read-Only register contains the frame start

marker byte of the 16 byte Trail Trace Buffer Message

that has been received from the Far-End Terminal, via

the TR byte-field within the incoming E3 frames. The

remaining bytes, of this Trail Trace Buffer Message

can be found in the RxTTB-1 through RxTTB-15 reg-

isters.

The data in this register is typically of the form [1, C6,

C5, C4, C3, C2, C1, C0]. The "1" in the MSB position

identifies this byte as being the frame start marker

RXE3 NR BYTE REGISTER (ADDRESS = 0X1A)

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

RxNR[7:0]

0000

000

RXE3 GC BYTE REGISTER (ADDRESS = 0X1B)

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

RxGC[7:0]

0000

000

RXE3 TTB-0 REGISTER (ADDRESS = 0X1C)

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

RxTTB-0

0000

000

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