DS21448L+ Maxim Integrated Products, DS21448L+ Datasheet - Page 31

• Manufacturer Part Number: DS21448L+
• Description: IC LIU QUAD E1/T1/J1 128-LQFP
• Manufacturer: Maxim Integrated Products
• Type: Line Interface Units (LIUs)r

Specifications of DS21448L+

• Number Of Drivers/receivers: 4/4
• Protocol: T1/E1/J1
• Voltage - Supply: 3.135 V ~ 3.465 V
• Mounting Type: Surface Mount
• Package / Case: 128-TQFP, 128-VQFP
• Product: Framer
• Number Of Transceivers: 4
• Supply Voltage (max): 3.465 V
• Supply Voltage (min): 3.135 V
• Supply Current (max): 400 mA
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.2 Loopbacks
6.2.1
When RLB (CCR6.6) is enabled, the DS21448 is placed into remote loopback. In this loopback, data from the
clock/data recovery state machine is looped back to the transmit path, passing through the jitter attenuator if it is
enabled. The data at the RPOS and RNEG pins is valid, while data presented at TPOS and TNEG is ignored. See
Figure 1-1
If the automatic RLB enable (CCR6.5) is set to 1, the DS21448 automatically goes 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 DS21448 detects the loop-down code programmed in the receive loop-down
code definition registers (RDNCD1 and RDNCD2) for a minimum of 5 seconds, the DS21448 comes out of remote
loopback. Setting ARLBE to 0 can also disable the ARLB.
6.2.2
When LLB (CCR6.7) is set to 1, the DS21448 is placed into local loopback. In this loopback, data on the transmit
side is transmitted as normal. TCLK and TPOS/TNEG pass through the jitter attenuator (if enabled) and are output
at RCLK and RPOS/RNEG. Incoming data from the line at RTIP and RRING is ignored. If transmit unframed all
ones (CCR3.7) is set to 1 while in LLB, TTIP and TRING transmit all ones while TCLK and TPOS/TNEG are looped
back to RCLK and RPOS/RNEG. See
6.2.3
Setting ALB (CCR6.4) to 1 puts the DS21448 in analog loopback. Signals at TTIP and TRING are internally
connected to RTIP and RRING. The incoming signals at RTIP and RRING are ignored. The signals at TTIP and
TRING are transmitted as normal. See
6.2.4
Setting CCR6.7 and CCR6.6 (LLB and RLB, respectively) to 1 puts the DS21448 into dual loopback operation. The
TCLK and TPOS/TNEG signals are looped back through the jitter attenuator (if enabled) and output at RCLK and
RPOS/RNEG. Clock and data recovered from RTIP and RRING are looped back to the transmit side and output at
TTIP and TRING. This mode of operation is not available when implementing hardware operation. See
more details.
6.3 PRBS Generation and Detection
Setting TPRBSE (CCR3.4) = 1 enables the DS21448 to transmit a 2
on the ETS bit setting in CCR1.7. The DS21448’s receive side always searches for these PRBS patterns
independently of CCR3.4. The PRBS bit-error output (PBEO) remains high until the receiver has synchronized to
one of the two patterns (64 bits received without an error), at which time PBEO goes low, and the PRBSD bit in the
SR is set. Once synchronized, any bit errors received cause a positive-going pulse at PBEO, synchronous with
RCLK. This output can be used with external circuitry track bit-error rates during the PRBS testing. Setting CCR6.2
(ECRS2) = 1 allows the PRBS errors to be accumulated in the 16-bit counter in registers ECR1 and ECR2. The
PRBS synchronizer remains in sync until it experiences six bit errors or more within a 64-bit span. Both PRBS
patterns comply with the ITU-T O.151 specifications.
6.4 Error Counter
Error count register 1 (ECR1) is the most significant word and ECR2 is the least significant word of a user-
selectable 16-bit counter that records incoming errors, including BPVs, code violations (CVs), excessive zero
violations (EXZs), and/or PRBS errors. See
Remote Loopback (RLB)
Local Loopback (LLB)
Analog Loopback (LLB)
Dual Loopback (DLB)
for more details.
Figure 1-1
Figure 1-1
Table
for more details.
for more details.
6-C,
31 of 60
Table
6-D, and
15
Figure 1-2
- 1 (E1) or a QRSS (T1) PRBS, depending
for details.
Figure 1-1