XRT83VSH28IB datasheet(35/74 Pages) EXAR

35 / 74 page

PRELIMINARY

XRT83VSH28

REV. P1.0.0

8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT

4.0

E1 APPLICATIONS

This applications section describes common E1 system considerations along with references to application

notes available for reference where applicable.

4.1

Loopback Diagnostics

The XRT83VSH28 supports several loopback modes for diagnostic testing. The following section describes

the local analog loopback, remote loopback, digital loopback, and dual loopback modes.

4.1.1

Local Analog Loopback

With local analog loopback activated, the transmit output data at TTIP/TRING is internally looped back to the

analog inputs at RTIP/RRING. External inputs at RTIP/RRING are ignored while valid transmit output data

continues to be sent to the line. A simplified block diagram of local analog loopback is shown in Figure 20.

FIGURE 20. SIMPLIFIED BLOCK DIAGRAM OF LOCAL ANALOG LOOPBACK

NOTE: The transmit diagnostic features such as TAOS and QRSS take priority over the transmit input data at TCLK/TPOS/

TNEG.

4.1.2

Remote Loopback

With remote loopback activated, the receive input data at RTIP/RRING is internally looped back to the transmit

output data at TTIP/TRING. The remote loopback includes the Receive JA (if enabled). The transmit input

data at TCLK/TPOS/TNEG are ignored while valid receive output data continues to be sent to the system. A

simplified block diagram of remote loopback is shown in Figure 21.

FIGURE 21. SIMPLIFIED BLOCK DIAGRAM OF REMOTE LOOPBACK

Encoder

Decoder

Timing

Control

Data and

Clock

Recovery

TAOS

QRSS

TTIP

TRING

RTIP

RRING

TCLK

TPOS

TNEG

RCLK

RPOS

RNEG