Datasheet

DS26521 Single T1/E1/J1 Transceiver
77 of 258
8.11.5 LIU Loopbacks
The DS26521 provides four LIU loopbacks for diagnostic purposes: analog loopback, local loopback, remote
loopback, and dual loopback. In the loopback diagrams that follow, TSER, TCLK, RSER, and RCLK are
inputs/outputs from the framer.
8.11.5.1 Analog Loopback
The analog output of the transmitter TTIP and TRING is looped back to RTIP and RRING of the receiver. Data at
RTIP and RRING is ignored in analog loopback. This is shown in
Figure 8-22.
Figure 8-22. Analog Loopback
LINE
DRIVER
TRANSMIT
FRAMER
TCLK
RECEIVE
FRAMER
OPTIONAL
JITTER
ATTENUATOR
RECEIVE
DIGITAL
RECEIVE
ANALOG
RCLK
RTIP
RRING
TSER
RSER
OPTIONAL
JITTER
ATTENUATOR
TRANSMIT
ANALOG
TRANSMIT
DIGITAL
8.11.5.2 Local Loopback
The transmit system data (the internal signals TTIP, TRING, and TCLK) is looped back to receive-side inputs to the
receive jitter attenuator. The data is also output on TTIP and TRING. Signals at RTIP and RRING are ignored. This
loopback is conceptually shown in
Figure 8-23.
Figure 8-23. Local Loopback
LINE
DRIVER
TRANSMIT
FRAMER
TRANSMIT
ANALOG
TCLK
TSER
OPTIONAL
JITTER
ATTENUATOR
RCLK
RSER
RTIP
RRING
TTIP
TRING
RECEIVE
ANALOG
RECEIVE
DIGITAL
TRANSMIT
DIGITAL
OPTIONAL
JITTER
ATTENUATOR
RECEIVE
FRAMER