
XRT86SH221
PRELIMINARY
103
SDH-TO-PDH FRAMER/MAPPER WITH INTEGRATED 21-CHANNEL E1 SH LIU
REV. P1.0.5
5.3.4
RLOS (Receiver Loss of Signal)
The LIU section supports both G.775 or ETSI-300-233 RLOS detection.
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.
5.3.5
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. By default, EXLOS is disabled and RLOS
operates in normal mode.
5.3.6
Jitter Attenuator
The jitter attenuator reduces phase and frequency jitter in the recovered clock if it is selected in the receive
path. 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. 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 of the FIFO bit depth.
N
OTE
:
If the LIU is used in a multiplexer/mapper application where stuffing bits are typically removed, the jitter attenuator
can be selected in the transmit path to smooth out the gapped clock. See the Transmit LIU Section of this
datasheet.
5.3.7
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 RPOS "Low" to prevent data
chattering to the internal connection to the VT Mapper section. 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 54
.
F
IGURE
54. S
IMPLIFIED
B
LOCK
D
IAGRAM
OF
THE
R
X
MUTE F
UNCTION
RLOS
RxMUTE
RPOS