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DS3171/DS3172/DS3173/DS3174
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highlights where each loopback mode is located and gives an overall view of the various loopback
paths available.
Figure 10-10. Loopback Modes
DS3/E3
Transmit
LIU
IEEE P1149.1
JTAG Test
Access Port
Microprocessor
Interface
HDLC
FEAC
LL
B
DLB
DS3 / E3
Transmit
Formatter
DS3 / E3
Receive
Framer
Trail
Trace
Buffer
DS3/E3
Receive
LIU
TAIS
TUA1
Clock Rate
Adapter
TX BERT
RX BERT
PL
B
ALB
UA1
GEN
B3ZS/
HDB3
Encoder
B3ZS/
HDB3
Decoder
10.5.1.1 Analog Loopback (ALB)
Analog loopback is enabled by setting
LBM[2:0] = 001. Analog loopback mode will not be enabled
when the port is configured for loop-timed mode (set via the
LOOPT bit).
The analog loopback is a loopback as close to the pins as possible. When both the TX and RX LIU are enabled, it
loops back TXPn and TXNn to RXPn and RXNn, respectively. If the transmit signals on TXPn and TXNn are not
terminated properly, this loopback path may have data errors or loss of signal. When the LIU is not enabled, it
loops back TLCLKn,TPOSn / TDATn,TNEGn to RLCLKn, RPOSn / RDATn , RNEGn.
Figure 10-11. ALB Mux
RXP
RXN
TXP
TXN
RX
LIU
TX
LIU