XRT7250 datasheet(345/463 Pages) EXAR

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XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

326

• If the XRT7250 Framer IC detects 2 consecutive E3

frames that each contain 8 or more “0’s”.

Enabling and Disabling the Change in Receive

AIS Condition Interrupt

The user can enable or disable the Change in Re-

ceive LOS Condition Interrupt, by writing the appro-

priate value into Bit 0 (AIS Interrupt Enable), within

the RxE3 Interrupt Enable Register - 1, as indicated

below.

Setting this bit-field to “1” enables this interrupt. Con-

versely, setting this bit-field to “0” disables this inter-

rupt.

Servicing the Change in Receive AIS Condition

Interrupt

Whenever the XRT7250 Framer IC detects this inter-

rupt, it will do all of the following.

• It will assert the Interrupt Request output pin (INT),

by driving it “Low”.

• It will set Bit 0 (AIS Interrupt Status), within the Rx

E3 Interrupt Status Register - 1 to “1”, as indicated

below.

Whenever the user’s system encounters the Change

in Receive AIS Condition Interrupt, then it should do

the following.

1. It should determine the current state of the AIS

condition. Recall, that this interrupt can be gen-

erated, whenever the XRT7250 Framer IC

declares or clears the AIS defect. Hence, the

user can determine the current state of the AIS

defect by reading the state of Bit 3 (RxAIS) within

the Rx E3 Configuration and Status Register - 2,

as illustrated below.

If the AIS Condition is TRUE

1. It should begin transmitting the FERF indication

to the Remote Terminal Equipment. Please see

Section 4.2.4.2.1.3 for instructions on how to

transmit a FERF condition.

If the AIS Condition is FALSE

2. It should cease transmitting the FERF indication

to the Remote Terminal Equipment. Please see

Section 4.2.4.2.1.3 for instructions on how to con-

trol the state of the “A” bit-field, within each out-

bound E3 frame.

5.3.6.2.5

The Change of Framing Alignment

Interrupt

If the Change of Framing Alignment Interrupt is en-

abled then the XRT7250 Framer IC will generate an

interrupt any time the Receive E3 Framer block de-

tects an abrupt change of framing alignment.

NOTE: This interrupt is typically accompanied with the

Change in Receive OOF Condition interrupt as well.

Conditions causing the XRT7250 Framer IC to

generate this interrupt.

If the XRT7250 Framer detects receives at least four

consecutive E3 frames, within its Framing Alignment

bytes in Error, then the XRT7250 Framer IC will de-

clare an OOF condition. However, while the

XRT7250 Framer IC is operating in the OOF condi-

RXE3 INTERRUPT ENABLE REGISTER - 1 (ADDRESS = 0X12)

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

Not Used

COFA

Interrupt

Enable

OOF

Interrupt

Enable

LOF

Interrupt

Enable

LOS

Interrupt

Enable

AIS

Interrupt

Enable

R/W

000

RXE3 CONFIGURATION & STATUS REGISTER - 2 (ADDRESS = 0X11)

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

RxLOF

Algo

RxLOF

RxOOF

RxLOS

RxAIS

Not Used

RxFERF

R/W

RORO

RORORORO

100

111

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