XRT7250 datasheet(451/463 Pages) EXAR

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XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

432

1. When the XRT7250 Framer IC declares an LOF

(Out of Frame) Condition, and

2. When the XRT7250 Framer IC clears the LOF

condition.

Conditions causing the XRT7250 Framer IC to de-

clare an LOF Condition.

• If the Receive E3 Framer block (within the XRT7250

Framer IC) detects Framing Byte errors, within four

consecutive incoming E3 frames and is not able to

transition back into the In-Frame state within 1 or

3ms.

Conditions causing the XRT7250 Framer IC to

clear the LOF Condition.

• If the Receive E3 Framer block transitions from the

OOF Condition state to the LOF Condition state

(see Figure 175).

• If the Receive E3 Framer block transitions back into

the In-Frame state.

Enabling and Disabling the Change in Receive

LOF Condition Interrupt

The user can enable or disable the Change in Re-

ceive LOF Condition Interrupt, by writing the appropri-

ate value into Bit 3 (LOF Interrupt Enable), within the

RxE3 Interrupt Enable Register - 1, as indicated be-

low.

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 LOF 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 6 (LOF Interrupt Status), within the Rx

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

below.

6.3.6.2.4

The Change of Framing Alignment

(COFA) 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-

tion, it will still rely on the old framing alignment for E3

payload data extraction, etc.

However, if the Receive E3 Framer had to change

alignment, in order to re-acquire frame synchroniza-

tion, then this interrupt will occur.

Enabling and Disabling the Change of Framing

Alignment Interrupt

The user can enable or disable the Change of Fram-

ing Alignment Interrupt by writing the appropriate val-

ue into Bit 4 (COFA Interrupt

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

Rx LOF Algo

RxLOF

RxOOF

RxLOS

RxAIS

RxPld Unstab

TMark

RxFERF

R/W

RORO

RORORORO

XXXX

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