XRT7250 datasheet(103/463 Pages) EXAR

103 / 463 page

XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

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.

2.3.4.9

Receive E3 Service Bits Register (E3,

ITU-T G.751)

Bit 1 - RxA (A-Bit)

This Read-Only bit-field reflects the state of the “A”

bit-field, within the most recently received E3 frame.

Bit 0 - RxN (N-Bit)

This Read-Only bit-field reflects the state of the “N”

bit-field, within the most recently received E3 frame.

2.3.5

Transmit DS3 Configuration Registers

2.3.5.1

Transmit DS3 Configuration Register

(DS3 Applications)

Bit 7 - Tx Yellow Alarm

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

mand the Transmit DS3 Framer to transmit a Yellow

Alarm (e.g., X bits are all "0") in the outbound DS3

data stream.

Writing a "0" to this bit-field disables this feature (the

default condition). In this condition, the X-bits in the

out-bound DS3 frame, are internally generated

(based upon receiver conditions).

Writing a "1" to this bit-field invokes this command. In

this condition, the Transmit DS3 Framer will override

the internally-generated X-bits and force all of the X-

bits of each outbound DS3 frame to "0".

NOTE: For more information in this feature, please see Sec-

tion 3.2.4.2.1.1.

NOTE: This bit-setting is ignored if Bits 3, 4 or 5 (within this

Bit 6 - Tx X-Bit (Force X bits to "1")

This "Read/Write" bit-field permits the user to com-

mand the Transmit DS3 Framer to force all of the X-

bits, in the outbound DS3 Frames, to "1".

Writing a "0" to this bit-field disables this feature (the

default condition). In this case, the Transmit DS3

Framer will generate X-bits based upon the receive

conditions.

Writing a "1" to this bit-field invokes this command. In

this case, the Transmit DS3 Framer will overwrite the

internally-generated X-bits and set them all to "1".

NOTE: For more information on this feature, please see

Section 3.2.4.2.1.2.

NOTE: This bit-setting is ignored if Bits 3, 4, 5, or 7 (within

this register) are set to "1".

Bit 5 - Tx Idle (Pattern)

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

mand the Transmit DS3 Framer to transmit the Idle

Condition pattern. If the user invokes this command,

then the Transmit DS3 Framer will force the outbound

DS3 Frames to have the following patterns.

• Valid M-bits, F-bits and P-bits

• The three CP-Bits (F-frame #3) are "0"

• The X-bits are set to "1"

• A repeating "1100..." pattern in written into the pay-

load portion of the DS3 Frames.

RXE3 SERVICE BIT REGISTER (ADDRESS = 0X1A)

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

Not Used

RxA

RxN

000

TRANSMIT DS3 CONFIGURATION REGISTER (ADDRESS = 0X30)

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

Tx Yellow

Alarm

Tx X Bits

Tx Idle

Tx AIS

Tx LOS

FERF on

LOS

FERF on

OOF

FERF on

AIS

R/W

000

111

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