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XRT79L71
PRELIMINARY
365
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
signal (via the E3CLK input pin) and it (2) will output ether one of these clock signals to the Clock and Data
Recovery block (depending upon whether the XRT79L71 has been configured to operate in the DS3 or E3
Mode).
In some applications there may be a desire to externally use the 44.736MHz or 34.368MHz clock signal that is
synthesized by the "SFM Synthesizer" block elsewhere in the user's board design. If this is the case, then the
XRT79L71 can support this requirement.
The XRT79L71 includes a pin (or ball) that is called "CLKOUT" (Ball K16). This output pin can be configured to
output the 44.736MHz/34.368MHz clock signal that is synthesized by the "SFM Synthesizer" block.
Invoke this feature by setting Bit 6 (SFM Clock Out Enable), within the "LIU Channel Control" Register, to "1"
as depicted below.
Once the user sets this bit-field to "1", then the output driver (associated with the CLKOUT pin) will become
active, and either a 44.736MHz or 34.368MHz clock signal (depending upon whether the XRT79L71 has been
configured to operate in the DS3 or E3 Mode) will be output via this pin.
5.3.1.6
The LOS Declaration and Clearance Criteria for E3 Applications
The Receive DS3/E3 LIU Block consists of a special type of LOS (Loss of Signal) Detectors that was
specifically designed in order to insure that it declares and clears the LOS defect per the requirements in ITU-
T G.775.
More specifically when the XRT79L71 is operating in the "E3 Mode", then the Receive DS3/E3 LIU Block will
declare the LOS defect Condition if the signal amplitude drops to -35dB or below (where 0dB pertains to an E3
pulse that is of amplitude 1Vpk). Further, the Receive DS3/E3 LIU Block device will clear the LOS defect
Condition if the signal amplitude rises back up to -15dB or above. Figure 169 presents an illustration that
depicts the signal levels at which the Receive DS3/E3 LIU Block will declare and clear the LOS defect.
LIU Channel Control Register (Address = 0x1306)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
SFM
Clock Out
Enable
SFM
Enable
LIU
Remote
Loop-back
Mode
LIU
Local
Loop-back
Mode
Unused
R/O
R/W
R/O
0
1
0