ds2149qt-r Maxim Integrated Products, Inc., ds2149qt-r Datasheet - Page 20

• Manufacturer Part Number: ds2149qt-r
• Description: Ds2149 5v T1/j1 Line Interface Unit
• Manufacturer: Maxim Integrated Products, Inc.

DS2149
10.1 Loopback Modes
10.1.1 Local Loopback (LLB)
When local loopback is enabled (set LLB in CR2, or pull the LLB pin high), inbound data at the receiver
inputs are ignored. TCLK and TPOS/TNEG pass through the jitter attenuator if enabled and are output at
RCLK and RPOS/RNEG. The transmit path is unaffected by LLB, and will continue to transmit data
normally (or AIS if TAIS is enabled).
10.1.2 Analog Loopback (ALB)
When analog loopback (ALB) is enabled (set ALB in CR2, or float the LLB pin), the receiver input pins
are disconnected from the clock and data recovery circuit and replaced by TTIP and TRING. This tests
the entire device including the jitter attenuator, transmitter, and receiver circuits.
10.1.3 Remote Loopback (RLB)
When remote loopback (RLB) is enabled (set RLB in CR2, or pull RLB pin high), inbound data at the
receiver inputs is looped back to the transmitter path. Data passes through the jitter attenuator if enabled.
The B8ZS encoder and decoder are not included in the loopback path. The receive path continues to
operate normally.
10.1.4 Network Loopback
When ENLOOP is enabled (set ENLOOP in CR2, or float the ENLOOP pin), the in-band loop code
detector is enabled. The receiver detects the in-band loop code patterns (00001 = loop up and
001 = loop down) present in the inbound data. The detectors detect both framed and unframed loop codes.
When the loop-up pattern is detected and present for 5 seconds, the device invokes remote loopback.
ENLOOP is dropped when:
1) The in-band loop-down pattern is present for 5 seconds.
2) RLB is activated.
3) ALB is activated.
10.1.5 Dual Loopback
Dual loopback is the simultaneous enabling of RLB and LLB. If the jitter attenuator is enabled and, when
both loopback paths are enabled, the jitter attenuator is placed in the local loopback path.
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