XRT83L34_05 Datasheet, PDF (48/99 Pages) Exar Corporation – QUAD T1/E1/J1 LH/SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR

XRT83L34
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REV. 1.0.1 QUAD T1/E1/J1 LH/SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR
transition of NLCD. The host has the option to ignore the request from the remote terminal, or to respond to the
request and manually activate Remote Loop-Back. The host can subsequently activate the detection of the
Loop-Down Code by setting NLCDE1=”1” and NLCDE0=”0”. In this case, receiving the “001” Loop-Down Code
for longer than 5 seconds will set the NLCD bit to “1” and if the NLCD interrupt is enabled, the chip will initiate
an interrupt on every transition of NLCD. The host can respond to the request from the remote terminal and
remove Loop-Back condition. In the manual Network Loop-Up (NLCDE1=”0” and NLCDE0=”1”) and Loop-
Down (NLCDE1=”1” and NLCDE0=”0”) Code detection modes, the NLCD interface bit will be set to “1” upon
receiving the corresponding code in excess of 5 seconds in the receive data. The chip will initiate an interrupt
any time the status of the NLCD bit changes and the Network Loop-code interrupt is enabled.
In the Host mode, setting the interface bits NLCDE1=”1” and NLCDE0=”1” enables the automatic Loop-Code
detection and Remote Loop-Back activation mode if, TXTEST[2:0] is NOT equal to “110”. As this mode is
initiated, the state of the NLCD interface bit is reset to “0” and the chip is programmed to monitor the receive
input data for the Loop-Up Code. If the “00001” Network Loop-Up Code is detected in the receive data for
longer than 5 seconds in addition to the NLCD bit in the interface register being set, Remote Loop-Back is
automatically activated. The chip stays in remote Loop-Back even if it stops receiving the “00001” pattern. After
the chip detects the Loop-Up code, sets the NLCD bit and enters Remote Loop-Back, it automatically starts
monitoring the receive data for the Loop-Down code. In this mode however, the NLCD bit stays set even if the
receiver stops receiving the Loop-Up code, which is an indication to the host that the Remote Loop-Back is still
in effect. Remote Loop-Back is removed if the chip detects the “001” Loop-Down code for longer than 5
seconds. Detecting the “001” code also results in resetting the NLCD interface bit and initiating an interrupt.
The Remote Loop-Back can also be removed by taking the chip out of the Automatic detection mode by
programming it to operate in a different state. The chip will not respond to remote Loop-Back request if Local
Analog Loop-Back is activated locally. When programmed in Automatic detection mode the NLCD interface bit
stays “High” for the whole time the Remote Loop-Back is activated and initiates an interrupt any time the status
of the NLCD bit changes provided the Network Loop-code interrupt is enabled.
TRANSMIT AND DETECT QUASI-RANDOM SIGNAL SOURCE (TDQRSS)
Each channel of XRT83L34 includes a QRSS pattern generation and detection block for diagnostic purposes
that can be activated only in the Host mode by setting the interface bits TXTEST2=”1”, TXTEST1=”0” and
TXTEST0=”0”. For T1 systems, the QRSS pattern is a 2²⁰-1pseudo-random bit sequence (PRBS) with no
more than 14 consecutive zeros. For E1 systems, the QRSS pattern is 2¹⁵ -1 PRBS with an inverted output.
With QRSS and Analog Local Loop-Back enabled simultaneously, and by monitoring the status of the QRPD
interface bit, all main functional blocks within the transceiver can be verified.
When the receiver achieves QRSS synchronization with fewer than 4 errors in a 128 bits window, QRPD
changes from “Low” to “High”. After pattern synchronization, any bit error will cause QRPD to go “Low” for one
clock cycle. If the QRPDIE bit is enabled, any transition on the QRPD bit will generate an interrupt.
With TDQRSS activated, a bit error can be inserted in the transmitted QRSS pattern by transitioning the
INSBER interface bit from “0” to “1”. Bipolar violation can also be inserted either in the QRSS pattern, or input
data when operating in the single-rail mode by transitioning the INSBPV interface bit from “0” to “1”. The state
of INSBER and INSBPV bits are sampled on the rising edge of the TCLK_n. To insure the insertion of the bit
error or bipolar violation, a “0” should be written in these bit locations before writing a “1”.
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