PRELIMINARY
XRT79L71
358
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The purpose of the Receive Equalizer block is to compensate for this "frequency-dependent" attenuation that
occurs within a DS3 or E3 signal, traveling via coaxial cable.
In essence, the Receive Equalizer block
accomplishes this by applying higher gain to higher frequency signals, than it does for lower frequency signals.
The Register Set, within the XRT79L71, permits the user to either enable or disable the Receive Equalizer,
within the Receive DS3/E3 LIU Block. In general, we strongly recommend that the user ALWAYS ENABLE the
Receive Equalizer block for all applications.
The user can enable the Receive Equalizer block by setting Bit 0 (Receive Equalizer Enable), within the "LIU
Receive Control" Register, to "1" as depicted below.
NOTE: By default, the Receive Equalizer block will (upon power up) be disabled. Therefore, the user MUST include
"enabling the Receive Equalizer block" as a part of the "start-up/configuration" procedure.
5.3.1.4
The Clock and Data Recovery Block
The purpose of the Clock and Data Recovery block (within the Receive DS3/E3 LIU Block) is two-fold.
To acquire and maintain "phase-lock" with the incoming DS3 or E3 line signal.
To insure that "downstream" circuitry, (such as the Receive DS3/E3 Framer block) is always provided with a
line-rate clock signal (to use as it timing reference).
Upon power-up, the Clock and Data Recovery block will attempt to acquire "phase-lock" with the incoming DS3
or E3 line signal. Once the Clock and Data Recovery block has acquired "lock" with the incoming DS3 or E3
signal, then it will indicate this fact by doing all of the following.
It will set Bit 2 (Receive LOL Defect Declared), within the "LIU Alarm Status"Register, to "0" as depicted
below.
It will generate the "Change of LOL (Loss of Lock) Defect Condition" Interrupt. The XRT79L71 will indicate
that it is generating this interrupt by (a) asserting the Interrupt Request output pin (by toggling it "LOW"), and
(b) by setting Bit 2 (Change of LOL Condition Interrupt), within the "LIU Interrupt Status" Register, to "1" as
depicted below.
LIU Receive Control Register (Address = 0x1305)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
Disable
DLOS
Detector
Disable
ALOS
Detector
Unused
LOSMUT
Enable
Receive
Monitor
Mode
Enable
Receive
Equalizer
Enable
R/O
R/W
R/O
R/W
0
1
LIU Alarm Status Register (Address = 0x1303)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
Digital
LOS
Defect
Declared
Analog
LOS
Defect
Declared
FL
(FIFO Limit)
Alarm
Declared
Receive
LOL
Defect
Declared
Receive
LOS Defect
Declared -
Receive
DS3/E3 LIU
Block
Transmit
DMO
Condition
R/O
0