XRT72L50 Datasheet, PDF (26/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. 1.2.1
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PIN DESCRIPTION
PIN #
70
PIN NAME
RLOOP
71
Req
72
GND
73
NC
74
RxLineClk
TYPE
O
O
****
I
DESCRIPTION
Remote Loopback Output Pin (to the XRT73L00 DS3/E3 Line Interface
Unit IC):
This output pin is intended to be connected to the RLOOP input pin of the
XRT73L00 DS3/E3 Line Interface Unit IC. The user can command this signal
to toggle "High" and, in turn, force the XRT73L00 DS3/E3 Line Interface Unit
IC into the Remote Loop-back mode. Conversely, the user can command this
signal to toggle "Low" and allow the XRT73L00 to operate in the normal
mode. (For a detailed description of the XRT73L00 DS3/E3 Line Interface
Unit IC's operation during Remote Loopback, please see the XRT73L00 DS3/
STS-1/ E3 Line Interface Unit IC's Data Sheet).
NOTE: If the customer is not using the XRT73L00 DS3/E3 Line Interface Unit
IC, then this output pin may be used for other purposes.
NOTE:
Receive Equalization Enable/Disable Select output pin - (to be con-
nected to the XRT73L00 DS3/E3 Line Interface Unit IC):
This output pin is intended to be connected to the REQ input pin of the
XRT73L00 DS3/E3 (REQDIS or REQEN of the XRT73L03 or XRT 73L04)
Line Interface Unit IC. The user can control the state of this output pin by writ-
ing a '0' or '1' to Bit 5 (REQ) within the Line Interface Driver Register (Address
= 0x80). If the user commands this signal to toggle "High" then the internal
Receive Equalizer (within the XRT73L00) will be disabled. Conversely, if the
user commands this output signal to toggle "Low", then the internal Receive
Equalizer (within the XRT73L00) will be enabled.
For information on the criteria that should be used when deciding whether to
bypass the equalization circuitry or not, please consult the XRT73L00 DS3/E3
Line Interface Unit data sheet.
NOTE: If the customer is not using the XRT73L00 DS3/E3 Line Interface Unit
IC, then this output pin may be used for other purposes.
Ground
No Connection
Receiver LIU (Recovered) Clock:
This input signal serves three purposes:
1. The Receive Framer uses it to sample and latch the signals at the RxPOS
and RxNEG input pins (into the Receive Framer circuitry).
2. This input signal functions as the timing reference for the Receive Framer
block.
3. The Transmit Framer block can be configured to use this input signal as its
timing reference.
This signal is the recovered clock from the external DS3/E3 LIU (Line Inter-
face Unit) IC, which is derived from the incoming DS3/E3 data.
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