LXT6155LE datasheet(16/50 Pages) INTEL

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LXT6155 — 155 Mbps SDH/SONET/ATM Transceiver

Datasheet

frames with incorrect frame words are required. Byte alignment occurs when entering the in-frame

state. In case of an OOF event, the byte alignment and frame pulse position are frozen. The ROFP

output continues unchanged until re-entering the in-frame state.

Figure 3. Framing State

2.2.2.1

Loss of Signal (LOS)

Loss of Signal provides an alarm signal indicating incoming signal voltage is weak or incoming

data does not contain enough transitions. This signal is available in HW mode on pin #45 and in

SW mode as status and interrupt (Reg #15, modes 00 and 05).

2.2.2.2

Coax Interface

Loss of Signal provides an alarm output that indicates weak line input signal. The LOS signal

asserts when the incoming signals fall below a specified loss threshold, and de-asserts when the

line signal rises nominally 2dB above the assert threshold. The threshold is adjustable in SW mode

(HWSEL = High) via the

µProcessor interface.

2.2.2.3

Fiber Interface

If no transition is detected during any 3112 bit times (20

µsec), LOS asserts. LOS is cleared when

two consecutive frame words with no LOS events between then are received. In SW mode

(HWSEL = High) the assertion window is programmable from 128 bits to 4096 bits in four steps.

The deassertion criteria can also be configured to 12.5% transition density. The 12.5% density is

determined by receipt of at least 4 transitions during a 32 bit sliding window.

Figure 4. Criteria for LOS Output

In Frame

4 consecutive frames

with errored FAS

2 consecutive frames

with correct FAS

Out of Frame

Nominal Value

LOS

De-assert

LOS

Assert

Level below nominal

HYS = 3 dB

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