Rainbow Electronics DS3170 - Manual (Page 72)

DS3170 DS3/E3 Single-Chip Transceiver
72 of 233
Figure 9-9 highlights where each loopback mode is located and gives an overall view of the various loopback paths
available.
Figure 9-9. Loopback Modes
DS3/E3
Transmit
LIU
IEEE P1149.1
JTAG Test
Access Port
Microprocessor
Interface
HDLC FEAC
LLB
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
9.5.1.1 Analog Loopback (ALB)
Analog loopback is enabled by setting PORT.CR4. LBM[2:0] = 001. Analog loopback mode will not be enabled
when the port is configured for loop timed mode (set via the PORT.CR3. LOOPT bit).
The analog loopback is a loopback as close to the pins as possible. When both the Tx and RX LIU is enabled, it
loops back TXP and TXN to RXP and RXN, respectively. If the transmit signals on TXP and TXN are not
terminated properly, this loopback path may have data errors or loss of signal. When the LIU is not enabled, it
loops back TLCLK,TPOS / TDAT,TNEG to RLCLK, RPOS / RDAT , RNEG.
Figure 9-10. ALB Mux
RXP
RXN
TXP
TXN
RX
LIU
TX
LIU