XRT83L34 Datasheet, PDF (42/82 Pages) Exar Corporation – QUAD T1/E1/J1 LH/SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR

XRT83L34
QUAD T1/E1/J1 LH/SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR
PRELIMINARY
REV. P1.3.4
LOOP-BACK MODES
The XRT83L34 supports several Loop-Back modes under both Hardware and Host control. In Hardware
mode the two LOOP[1:0] pins control the Loop-Back functions for each channel independently according to
Table 14.
TABLE 14: LOOP-BACK CONTROL IN HARDWARE MODE
LOOP1
LOOP0
LOOP-BACK MODE
0
0
None
0
1
Analog
1
0
Remote
1
1
Digital
In Host mode the Loop-Back functions are controlled by the three LOOP[2:0] interface bits. Each channel can
be programmed independently according to Table 15.
TABLE 15: LOOP-BACK CONTROL IN HOST MODE
LOOP2 LOOP1 LOOP0 LOOP-BACK MODE
0
X
X
None
1
0
0
Dual
1
0
1
Analog
1
1
0
Remote
1
1
1
Digital
LOCAL ANALOG LOOP-BACK (ALOOP)
With Local Analog Loop-Back activated, the transmit data at TTIP and TRING are looped-back to the analog
input of the receiver. External inputs at RTIP/RRING in this mode are ignored while valid transmit data
continues to be sent to the line. Local Analog Loop-Back exercises most of the functional blocks of the
XRT83L34 including the jitter attenuator which can be selected in either the transmit or receive paths. Local
Analog Loop-Back is shown in Figure 20.
FIGURE 20. LOCAL ANALOG LOOP-BACK SIGNAL FLOW
TPOS
TNEG
TCLK
RCLK
RPOS
RNEG
Encoder
Decoder
JA
Timing
Tx
Control
Data &
Clock
Rx
Recovery
TTIP
TRING
RTIP
RRING
In this mode, the jitter attenuator (if selected) can be placed in the transmit or receive path.
39