
XRT83VSH38
24
REV. 1.0.7
8-CHANNEL T1/E1/J1 SHORT-HAUL LINE INTERFACE UNIT
3.2.3.1
RLOS (Receiver Loss of Signal)
The XRT83VSH38 supports both G.775 or ETSI-300-233 RLOS detection scheme.
In G.775 mode, RLOS is declared when the received signal is less than 375mV for 32 consecutive pulse
periods (typical). The device clears RLOS when the receive signal achieves 12.5% ones density with no more
than 15 consecutive zeros in a 32 bit sliding window and the signal level exceeds 425mV (typical).
In ETSI-300-233 mode the device declares RLOS when the input level drops below 375mV (typical) for more
than 2048 pulse periods (1msec).
The device exits RLOS when the input signal exceeds 425mV (typical) and has transitions for more than 32
pulse periods with 12.5% ones density with no more than 15 consecutive zero’s in a 32 bit sliding window.
ETSI-300-233 RLOS detection method is only available in Host mode.
In T1 mode RLOS is declared when the received signal is less than 320mV for 175 consecutive pulse period
(typical). The device clears RLOS when the receive signal achieves 12.5% ones density with no more than 100
consecutive zeros in a 128 bit sliding window and the signal level exceeds 425mV (typical).
3.2.3.2
EXLOS (Extended Loss of Signal)
By enabling the extended loss of signal by programming the appropriate channel register, the digital RLOS is
extended to count 4,096 consecutive zeros before declaring RLOS in T1 and E1 mode. By default, EXLOS is
disabled and RLOS operates in normal mode.
3.2.3.3
AIS (Alarm Indication Signal)
The XRT83VSH38 adheres to the ITU-T G.775 specification for an all ones pattern. The alarm indication
signal is set to "1" if an all ones pattern (at least 99.9% ones density) is present for T, where T is 3ms to 75ms
in T1 mode. AIS will clear when the ones density is not met within the same time period T. In E1 mode, the
AIS is set to "1" if the incoming signal has 2 or less zeros in a 512-bit window. AIS will clear when the incoming
signal has 3 or more zeros in the 512-bit window.
3.2.3.4
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.
3.2.3.5
LCV (Line Code Violation)
The LIU contains 8 independent, 16-bit LCV counters. When the counters reach full-scale, they remain
saturated at FFFFh until they are reset globally or on a per channel basis. For performance monitoring, the
counters can be updated globally or on a per channel basis to place the contents of the counters into holding
registers. The LIU uses an indirect address bus to access a counter for a given channel. Once the contents of
the counters have been placed in holding registers, they can be individually read out 8-bits at a time according
to the BYTEsel bit in the appropriate global register. By default, the LSB is placed in the holding register until
the BYTEsel is pulled "High" where upon the MSB will be placed in the holding register for read back. Once
both bytes have been read, the next channel may be selected for read back.
By default, the LCV_OFD will be set to a "1" if the receiver is currently detecting line code violations or
excessive zeros for HDB3 (E1 mode) or B8ZS (T1 mode). In AMI mode, the LCV_OFD will be set to a "1" if the
receiver is currently detecting bipolar violations or excessive zeros. However, if the LIU is configured to
monitor the 16-bit LCV counter through software, the LCV_OFD will be set to a "1" if the counter saturates.
3.3
Receive Jitter Attenuator
The receive path has a dedicated jitter attenuator that reduces 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. 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-