XRT59L921 Datasheet, PDF (27/32 Pages) Exar Corporation – TWENTY-ONE CHANNEL E1 LINE INTERFACE UNIT

XRT59L921
REV. 1.2.1
TWENTY-ONE CHANNEL E1 LINE INTERFACE UNIT
indicator. In particular, the XRT59L921 will declare a LOS, between 10 and 255 UI (or E1 bit-periods) after the
actual time the LOS condition occurred. Further, the XRT59L921 will clear the LOS indicator within 10 to 255
UI after restoration of the incoming line signal. Figure 14 illustrates the LOS Declaration and Clearance
behavior, in response to first, the Loss of Signal event and then afterwards, the restoration of the signal.
FIGURE 14. THE BEHAVIOR OF THE LOS OUTPUT INDICATOR, IN RESPONSE TO THE LOSS OF SIGNAL, AND THE
RESTORATION OF THE SIGNAL
Actual Occurrence
of LOS Condition
Line Signal
is Restored
RxIN
Time Range for
LOS Declaration
10 UI
255 UI
10 UI
255 UI
LOS Output Pin
0 UI
G.775 Compliance
0UI
G.775 Compliance
Time Range for
LOS Clearance
2.6 LOS Mute Description
The LOSMute feature is included in the XRT59L921 such that when the input signal to a receiver is too low or
is lost. The LOS_n pin will toggle "High" and at the same time the RPOS_n and RNEG_n outputs are muted to
a "Zero" state to prevent output data chattering.
2.7 The Receive Output Interface block
The purpose of the Receive Output Interface block is to interface directly with the Receiving Terminal
Equipment. The Receive Output Interface block outputs the data (which has been recovered from the incoming
line signal) to the Receive Terminal Equipment via the RxPOS_n and RxNEG_n output pins.
If the Receive Sections of the XRT59L921 has received a Positive-Polarity pulse, via the RTIP_n and RRing_n
input pins, then the Receive Output Interface will output a pulse via the RxPOS_n output pins.
Similarly, if the Receive Sections of the XRT59L921 has received a Negative-Polarity pulse, via the RTIP_n
and RRing_n input pins, then the Receive Output Interface will output a pulse via the RxNEG_n output pins.
NOTE: The Receive Output Interface block does not supply a recovered clock. This device is intended to be used in those
applications, where the Clock Recovery circuit is realized in an ASIC solution.
3.0 SHUTTING OFF THE TRANSMITTER
Each channel (within the XRT59L921) permits the user to shut off the Transmit Driver within their respective
Transmit Section. This feature can come in handy for system redundancy design considerations or during
diagnostic testing. The user can activate this feature by connecting the TxClk_n input pin to a logic “0” (e.g.,
GND) and continue to apply data via the TxPOS_n and TxNEG_n input pins.
25