XRT91L32ES Exar, XRT91L32ES Datasheet - Page 16

• Manufacturer Part Number: XRT91L32ES
• Description: LIN Transceivers SONET SDH 8 bit TRANCEIVER
• Manufacturer: Exar

Specifications of XRT91L32ES

• Product Category: LIN Transceivers
• Rohs: yes

XRT91L32
STS-12/STM-4 OR STS-3/STM-1 SONET/SDH TRANSCEIVER
The clock and data recovery (CDR) unit accepts the high speed NRZ serial data from the Differential LVPECL
receiver and generates a clock that is the same frequency as the incoming data. The clock recovery can either
utilize the transmitter’s CMU reference clock from either REFCLKP/N or TTLREFCLK or it can use
independent clock source CDRAUXREFCLK to train and monitor its clock recovery PLL. Initially upon startup,
the PLL locks to the local reference clock within ±500 ppm. Once this is achieved, the PLL then attempts to
lock onto the incoming receive data stream. Whenever the recovered clock frequency deviates from the local
reference clock frequency by more than approximately ±500 ppm, the clock recovery PLL will switch and lock
back onto the local reference clock. Whenever a Loss of Lock or a Loss of Signal event occurs, the CDR will
continue to supply a receive clock (based on the local reference) to the framer/mapper device. When the
LOSEXT is asserted by the optical module or when LOS is detected, the receive parallel data output will be
forced to a logic zero state for the entire duration that a LOS condition is detected. This acts as a receive data
mute upon LOS function to prevent random noise from being misinterpreted as valid incoming data. When the
LOSEXT becomes inactive and the recovered clock is determined to be within ±500 ppm accuracy with respect
to the local reference source and LOS is no longer declared, the clock recovery PLL will switch and lock back
onto the incoming receive data stream. Table 5 shows Clock and Data Recovery reference clock settings.
Table 6 specifies the Clock and Data Recovery Unit performance characteristics.
CMUFREQSEL CDRREFSEL
2.3
1
2
accuracy required for SONET systems.
Requires frequency accuracy better than 20ppm in order for the transmitted data rate frequency to have the necessary
CDRAUXREFCLK requires accuracy of 77.76 MHz +/- 500ppm.
X
X
0
0
1
1
Receive Clock and Data Recovery
T
0
0
0
0
1
1
ABLE
5: C
LOCK
STS12/
STS3
0
1
0
1
0
1
D
ATA
R
not referenced by CDR
not referenced by CDR
ECOVERY UNIT REFERENCE CLOCK SETTINGS
F
REFCLKP/N
REQUENCY
TTLREFCLK
77.76 MHz
77.76 MHz
19.44 MHz
19.44 MHz
14
(MH
1
OR
1
Z
)
CDRAUXREFCLK
F
REQUENCY
77.76 MHz
77.76 MHz
not used
not used
not used
not used
(MH
Z
)
2
F
REQUENCY
xr
CDR O
155.52
622.08
155.52
622.08
155.52
622.08
UTPUT
REV. 1.0.2
(MH
Z
)