Datasheet

ADN8102
Rev. B | Page 20 of 36
LOOPBACK
The ADN8102 provides loopback on both input ports (Port A:
cable interface input, and Port B: line card interface input). The
external loopback toggle pin, LB, controls the loopback of the Port
B input only (board side loopback). When loopback is asserted,
valid data continues to pass through the Port B link, but the
Port B input signals are also shunted to the Port A output to allow
testing and debugging without disrupting valid data. This
loopback, as well as loopback of the Port A input (cable side
loopback), can be programmed through the I
2
C interface. The
loopbacks are controlled through the I
2
C interface by writing to
Bit 0 and Bit 1 of the loopback control register (Register 0x02).
Bit 0 represents loopback of the Port A inputs to the Port B
outputs (cable side loopback). Bit 1 represents loopback of the
Port B inputs to the Port A outputs (board side loopback), with
high representing loopback for both bits. Bit 1 can be overridden
by the LB pin if the pin mode register is set to enable loopback
via external pin as shown in Table 5. Both input ports can be
looped back simultaneously (full loopback) by writing high to
both Bit 0 and Bit 1, but in this case, valid data is disrupted on
each channel. Figure 40 illustrates the three loopback modes.
CONTROL LOGIC
TRANSMIT
PRE-EMPHASIS
RECEIVE
EQUALIZATION
EQ
Ix_B[3:0]
LB
A
DDR[1:0]
SCL
SDA
RESET
Ox_B[3:0]
LOS_A
Ix_A[3:0]
PE_A[1:0]
EQ_A[1:0]
EQ_B[1:0]
PE_B[1:0]
ENA
ENB
RECEIVE
EQUALIZATION
EQ
TRANSMIT
PRE-EMPHASIS
PE
PE
Ox_A[3:0]
CONTROL LOGIC
TRANSMIT
PRE-EMPHASIS
RECEIVE
EQUALIZA TION
EQ
Ix_B[3:0]
LB
ADDR[1:0]
SCL
SDA
RESET
Ox_B [3:0]
LOS_A
Ix_A[3:0]
PE_A[1:0]
EQ_A[1:0]
EQ_B[1:0]
PE_B[1:0]
ENA
ENB
RECEIVE
EQUALIZATION
EQ
TRANSMIT
PRE-EMPHASIS
PE
PE
Ox_A[3:0]
CONTROL LOGIC
TRANSMIT
PRE-EMPHASIS
RECEIVE
EQUALIZATION
EQ
Ix_B[3:0]
LB
ADDR[1:0]
SCL
SDA
RESET
Ox_B[3:0]
LOS_A
Ix_A[3:0]
PE_A[1:0]
EQ_A[1:0]
EQ_B[1:0]
PE_B[1:0]
ENA
ENB
RECEIVE
EQUALIZATION
EQ
TRANSMIT
PRE-EMPHASIS
PE
PE
Ox_A[3:0]
CABLE SIDE LOOPBACK BOARD SIDE LOOPBACK FULL LOOPBACK
07060-005
Figure 40. Loopback Modes of Operation
Table 12. Loopback Control Functionality
Control Mode
1
LB Pin LB[1] LB[0] Description
Pin Control (00 or 01) 0 X
2
X Loopback disabled
1 X X Board side loopback enabled
Serial Control X 0 0 Loopback disabled
(10 or 11) X 0 1 Cable side loopback enabled
X 1 0 Board side loopback enabled
X 1 1 Full loopback enabled
1
Refer to Table 5 for additional information regarding control mode settings.
2
X = don’t care.
Table 13. Loopback Control Register
Name Address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default
Loopback control 0x02 LB[1] LB[0] 0x00