XRT86L30
SINGLE T1/E1/J1 FRAMER/LIU COMBO
5.0 LOOPBACK MODES OF OPERATION
REV. 1.0.1
5.1
LIU Physical Interface Loopback Diagnostics
The XRT86L30 supports several loopback modes for diagnostic testing. The following section describes the
local analog loopback, remote loopback, digital loopback, and dual loopback modes. The LIU physical
interface loopback modes are independent from the Framer loopback modes. Therefore, it is possible to
configure multiple loopback modes creating tremendous flexibility within the looped diagnostic features.
5.1.1
Local Analog Loopback
With local analog loopback activated, the transmit output data at TTIP/TRING is internally looped back to the
analog inputs at RTIP/RRING. External inputs at RTIP/RRING are ignored while valid transmit output data
continues to be sent to the line. A simplified block diagram of local analog loopback is shown in Figure 27.
F
IGURE 27. SIMPLIFIED
B
LOCK
D
IAGRAM OF
L
OCAL
A
NALOG
L
OOPBACK
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
NOTE: The transmit diagnostic features such as TAOS, NLC generation, and QRSS take priority over the transmit input
data at TCLK/TPOS/TNEG.
5.1.2
Remote Loopback
With remote loopback activated, the receive input data at RTIP/RRING is internally looped back to the transmit
output data at TTIP/TRING. The remote loopback includes the Receive JA (if enabled). The transmit input
data at TCLK/TPOS/TNEG are ignored while valid receive output data continues to be sent to the system. A
simplified block diagram of remote loopback is shown in Figure 28.
F
IGURE 28. SIMPLIFIED
B
LOCK
D
IAGRAM OF
R
EMOTE
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
157
EXAR [ EXAR CORPORATION ]
