XRT86VL32IB datasheet(63/153 Pages) EXAR

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XRT86VL3X

REV. 1.2.2

T1/E1/J1 FRAMER/LIU COMBO - ARCHITECTURE DESCRIPTION

6.2.3

FLSD (FIFO Limit Status Detection)

The purpose of the FIFO limit status is to indicate when the Read and Write FIFO pointers are within a pre-

determined range (over-flow or under-flow indication). The FLSD is set to "1" if the FIFO Read and Write

Pointers are within ±3-Bits.

6.2.4

Receive Jitter Attenuator

The receive path has a dedicated jitter attenuator to reduce phase and frequency jitter in the recovered clock.

The jitter attenuator uses a data FIFO (First In First Out) with a programmable depth of 32-bit or 64-bit. If the

LIU is used for line synchronization (loop timing systems), the JA should be enabled in the receive path. When

the Read and Write pointers of the FIFO are within 2-Bits of over-flowing or under-flowing, the bandwidth of the

jitter attenuator is widened to track the short term input jitter, thereby avoiding data corruption. When this

condition occurs, the jitter attenuator will not attenuate input jitter until the Read/Write pointer’s position is

outside the 2-Bit window. In T1 mode, the bandwidth of the JA is always set to 3Hz. In E1 mode, the

bandwidth is programmable to either 10Hz or 1.5Hz (1.5Hz automatically selects the 64-Bit FIFO depth). The

JA has a clock delay equal to ½ of the FIFO bit depth.

NOTE: The Transmit Path has a dedicated jitter attenuator. See the Transmit Path Line Interface Section.

6.2.5

RxMUTE (Receiver LOS with Data Muting)

The receive muting function can be selected by setting RxMUTE to "1" in the appropriate global register. If

selected, any channel that experiences an RLOS condition will automatically pull the output of the LIU section

"Low" to prevent data chattering. If RLOS does not occur, the RxMUTE will remain inactive until an RLOS on a

given channel occurs. The default setting for RxMUTE is "0" which is disabled. A simplified block diagram of

the RxMUTE function is shown in Figure 60.

FIGURE 59. PROCESS BLOCK FOR AUTOMATIC LOOP CODE DETECTION

Automatic Remote

Loopback

Loop-Up

Code for

5 sec?

Yes

Loop-Down

Code for

5 sec?

Yes

Disable Remote

Loopback

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