XRT59L921 Datasheet, PDF (18/32 Pages) Exar Corporation – TWENTY-ONE CHANNEL E1 LINE INTERFACE UNIT

XRT59L921
TWENTY-ONE CHANNEL E1 LINE INTERFACE UNIT
REV. 1.2.1
FIGURE 4. ILLUSTRATION ON HOW THE XRT59L921 SAMPLES THE DATA ON THE TXPOS_N AND TXNEG_N INPUT
PINS
TxPOS_n
T_su
T_ho
TxNEG_n
TClk_n
In general, if the XRT59L921 samples a “1” on the TxPOS_n input pin, then the Transmit Section of the device
will ultimately generate a positive polarity pulse via the TTIP_n and TRing_n output pins (across a 1:2 trans-
former). Conversely, if the XRT59L921 samples a “1” on the TxNEG_n input pin, then the Transmit Section of
the device will ultimately generate a negative polarity pulse via the TTIP_n and TRing_n output pins (across a
1:2 transformer).
1.2.1 Operating the Transmitter in the Clockless Mode
The user can configure a given channel (within theXRT59L921) to operate in the Clockless mode by doing the
following:
• Not applying a clock signal to the TxClk_n input, and pulling this pin to VDD.
• By applying RZ (Return to Zero) data to the TxPOS_n and TxNEG_n input pins, as illustrated below.
• If TxClk_n is grounded and RZ data is applied to TPOS and TNEG, the transmitter will be
powered down and tri-stated.
1.2.2 Shutting off the Transmiter
The Transmit Driver for each Channel_n (within the XRT59L921) can be shut off. To activate this feature,
Connect 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.
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