LXT351 — T1/E1 Short Haul Transceiver with Crystal-less Jitter Attenuation
2.5
Diagnostic Mode Operation
The LXT351 offers multiple diagnostic modes as listed in Table 4. The diagnostic modes are
selected by setting the appropriate register bits as described in the following paragraphs.
2.5.1
Loopback Modes
Local Loopback
2.5.1.1
See Figure 4 and Figure 5. Local loopback is selected by setting CR2.ELLOOP to 1. LLOOP
inhibits the receiver circuits. The transmit clock and data inputs (TCLK and TPOS/TNEG or
TDATA) loop back through the jitter attenuator (if enabled) and show up at RCLK and RPOS/
RNEG or RDATA. Note that during LLOOP, the JASEL input is strictly an Enable/Disable control;
it does not affect the placement of the JAL. If JA is enabled, it is active in the loopback circuit. If
JA is bypassed, it is not active in the loopback circuit.
The transmitter circuits are unaffected by LLOOP. LXT351 transmits the TPOS/TNEG or TDATA
inputs (or a stream of 1s if TAOS is asserted) normally. When used in this mode, the transceiver
can function as a stand-alone jitter attenuator.
Figure 4. Local Loopback
Table 4. Diagnostic Mode Summary
Interrupt
Maskable
Diagnostic Mode
Loopback Modes
Local Loopback (LLOOP)
Analog Loopback (ALOOP)
Remote Loopback (RLOOP)
Dual Loopback (DLOOP)
No
No
No
No
16
Datasheet
INTEL [ INTEL ]
