XRT7250 datasheet(213/463 Pages) EXAR

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XRT7250

DS3/E3 FRAMER IC

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REV. 1.1.1

194

if the number of AIS-type M-frames is detected, such

that it meets the following conditions:

NAIS - NVALID > 63

where:

NAIS = the number of M-frames containing the AIS

pattern.

NVALID = the number of M-frames not containing the

AIS pattern

If at anytime, the contents of this Up/Down counter

exceeds 63 M-frames, then the Receive DS3 Framer

block will:

1. Assert the RxAIS output pin by toggling it "High".

2. Set Bit 7 (RxAIS) within the Rx DS3 Configuration

and Status Register, to "1" as depicted below.

3. Generate a Change in AIS Status Interrupt

Request to the µP/µC.

4. Force the Transmit Section to transmit a FERF

indication back to the remote terminal.

The Receive DS3 Framer block will clear the AIS con-

dition when the following expression is true.

NAIS - NVALID < 0.

In other words, once the Receive DS3 Framer block

has detected a sufficient number of normal (or Non-

AIS) M-frames, such that this Up/Down counter

reaches zero, then the Receive DS3 Framer block will

clear the AIS Condition indicators. The Receive DS3

Framer block will inform the µC/µP of this negation of

the AIS Status by generating a Change in AIS Status

interrupt.

4.3.2.5.3

The Idle (Condition) Alarm

The Receive DS3 Framer block will identify and de-

clare an Idle Condition if it receives a sufficient num-

ber of M-Frames that meets all of the following condi-

tions.

• Valid M-bits, F-bits, and P-bits

• The 3 CP-bits (in F-Frame #3) are zeros.

• The X-bits are set to 1

• The payload portion of the DS3 Frame exhibits a

repeating 1100... pattern.

The Receive DS3 Framer block circuitry includes an

Up/Down Counter that is used to track the number of

M-frames that have been identified as exhibiting the

Idle Condition by the Receive DS3 Framer block. The

contents of this counter are set to zero upon reset or

power up. This counter is then incremented whenev-

er the Receive DS3 Framer block detects an Idle-type

M-frame. The counter is decremented, or kept at ze-

ro if a non-Idle M-frame is detected. If the Receive

DS3 Framer block detects a sufficient number of Idle-

type M-frames, such that the counter reaches the

number 63, then the Receive DS3 Framer block will

declare the Idle Condition. Explained another way,

the Receive DS3 Framer block will declare an Idle

Condition if the number of Idle-Pattern M-frames is

detected such that it meets the following conditions.

NIDLE - NVALID > 63,

where:

NIDLE = the number of M-frames containing the Idle

Pattern

NVALID = the number of M-frames not exhibit the Idle

Pattern

Anytime the contents of this Up/Down Counter reach-

es the number 63, then the Receive DS3 Framer

block will:

1. Set Bit 5 (RxIdle) within the Rx DS3 Configuration

and Status Register, to "1" as depicted below.

RX DS3 CONFIGURATION AND STATUS REGIS-

TER, (ADDRESS = 0X10)

RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)

BIT 7BIT 6BIT 5BIT 4BIT 3BIT2BIT 1BIT 0

RxAIS

RxLOS

RxIdle

RxOOF

Int LOS

Disable

Framing on

Parity

F-Sync Algo

M-Sync Algo

XXXX

RX DS3 CONFIGURATION AND STATUS REGISTER, (ADDRESS = 0X10)

BIT 7BIT 6

BIT 5BIT 4BIT 3BIT2BIT 1BIT 0

RxAIS

RxLOS

RxIdle

RxOOF

Int LOS

Disable

Framing on

Parity

F-Sync Algo

M-Sync Algo

R/O

R/W

XXX

XRT7250 Datasheet(PDF) 213 Page - Exar Corporation

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