XRT86L30
REV. 1.0.1
SINGLE T1/E1/J1 FRAMER/LIU COMBO
5.1.3
Digital Loopback
With digital loopback activated, the transmit input data at TCLK/TPOS/TNEG is looped back to the receive
output data at RCLK/RPOS/RNEG. The digital loopback mode includes the Transmit JA (if enabled). The
receive input data at RTIP/RRING is ignored while valid transmit output data continues to be sent to the line. A
simplified block diagram of digital loopback is shown in Figure 29.
F
IGURE 29. SIMPLIFIED
B
LOCK
D
IAGRAM OF
D
IGITAL LOOPBACK
NLC/PRBS/QRSS
Encoder
TAOS
TCLK
TPOS
TNEG
Timing
Control
TTIP
TRING
JA
JA
Tx
RCLK
RPOS
RNEG
Data and
Clock
Recovery
RTIP
RRING
Decoder
Rx
5.1.4
Dual Loopback
With dual loopback activated, the remote loopback is combined with the digital loopback. A simplified block
diagram of dual loopback is shown in Figure 30.
F
IGURE 30. SIMPLIFIED
B
LOCK
D
IAGRAM OF
D
UAL
LOOPBACK
NLC/PRBS/QRSS
Encoder
TAOS
TCLK
TPOS
TNEG
Timing
Control
TTIP
TRING
JA
JA
Tx
RCLK
RPOS
RNEG
Data and
Clock
Recovery
RTIP
RRING
Decoder
Rx
5.1.5
Framer Remote Line Loopback
The Framer Remote Line Loopback is almost identical to the LIU physical interface Remote Loopback. The
digital data enters the framer interface, however does not enter the framing blocks. The main difference
between the Remote loopback and the Framer Remote Line loopback is that the receive digital data from the
LIU is allowed to pass through the LIU Decoder/Encoder circuitry before returning to the line interface. A
simplified block diagram of framer remote line loopback is shown in Figure 31.
F
IGURE 31. SIMPLIFIED
B
LOCK
D
IAGRAM OF THE
F
RAMER
R
EMOTE LINE LOOPBACK
NLC/PRBS/QRSS
Encoder
TAOS
Framer
Tx
Timing
Control
TTIP
TRING
JA
JA
Tx
Data and
Clock
Recovery
RTIP
RRING
Framer
Rx
Decoder
Rx
158
EXAR [ EXAR CORPORATION ]
