XRT83SL28
xr
8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT
REV.1.0.0
3.0 E1 APPLICATIONS
This applications section describes common E1 system considerations along with references to application
notes available for reference where applicable.
3.1
Loopback Diagnostics
The XRT83SL28 supports several loopback modes for diagnostic testing. The following section describes the
local analog loopback, remote loopback, and digital loopback.
3.1.1
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 18.
FIGURE 18. SIMPLIFIED BLOCK DIAGRAM OF LOCAL ANALOG LOOPBACK
TAOS
TCLK
TPOS
TNEG
Timing
Control
TTIP
TRING
Encoder
Decoder
JA
JA
Tx
RCLK
RPOS
RNEG
Data and
Clock
Recovery
RTIP
RRING
Rx
NOTE: TAOS takes priority over the transmit input data at TPOS/TNEG.
3.1.2
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 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 19.
FIGURE 19. SIMPLIFIED BLOCK DIAGRAM OF REMOTE LOOPBACK
TAOS
TCLK
TPOS
TNEG
Timing
Control
TTIP
TRING
Encoder
Decoder
JA
JA
Tx
RCLK
RPOS
RNEG
Data and
Clock
Recovery
RTIP
RRING
Rx
NOTE: Remote Loop Back takes priority over TAOS.
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EXAR [ EXAR CORPORATION ]
