Datasheet

DS2148/DS21Q48
43 of 73
RDNCD2 (10H): RECEIVE DOWN CODE DEFINITION REGISTER 2
(MSB) (LSB)
C15 C14 C13 C12 C11 C10 C9 C8
SYMBOL POSITION DESCRIPTION
C15 RDNCD2.7
Receive Down Code Definition Bit 15
C14 RDNCD2.6
Receive Down Code Definition Bit 14
C13 RDNCD2.5
Receive Down Code Definition Bit 13
C12 RDNCD2.4
Receive Down Code Definition Bit 12
C11 RDNCD2.3
Receive Down Code Definition Bit 11
C10 RDNCD2.2
Receive Down Code Definition Bit 10
C9 RDNCD2.1
Receive Down Code Definition Bit 9
C8 RDNCD2.0
Receive Down Code Definition Bit 8
6.2 Loopbacks
6.2.1 Remote Loopback (RLB)
When RLB (CCR6.6) is enabled, the DS2148 is placed into remote loopback. In this loopback, data from
the clock/data recovery state machine will be looped back to the transmit path passing through the jitter
attenuator if it is enabled. The data at the RPOS and RNEG pins will be valid while data presented at
TPOS and TNEG will be ignored (Figure 1-1).
If the Automatic Remote Loopback Enable (CCR6.5) is set to a one, the DS2148 will automatically go
into remote loopback when it detects the loop up code programmed in the Receive Up Code Definition
Registers (RUPCD1 and RUPCD2) for a minimum of 5 seconds. When the DS2148 detects the loop
down code programmed in the Receive Loop Down Code Definition registers (RDNCD1 and RDNCD2)
for a minimum of 5 seconds, the DS2148 will come out of remote loopback. Setting ARLBE to a zero
also can disable the ARLB.
6.2.2 Local Loopback (LLB)
When LLB (CCR6.7) is set to a one, the DS2148 is placed into local loopback. In this loopback, data on
the transmit-side will continue to be transmitted as normal. TCLK and TPOS/TNEG will pass through the
jitter attenuator (if enabled) and be output at RCLK and RPOS/RNEG. Incoming data from the line at
RTIP and RRING will be ignored. If Transmit Unframed All Ones (CCR3.7) is set to a one while in LLB,
TTIP and TRING will transmit all ones while TCLK and TPOS/TNEG will be looped back to RCLK and
RPOS/RNEG (Figure 1-1).