XRT59L91 Datasheet, PDF (19/28 Pages) Exar Corporation – Single-Chip E1 Line Interface Unit

Preliminary
XRT59L91
The user can configure the XRT59L91 device to oper-
ate in the “Local Loop-back” Mode, by pulling the
“LLoop” input pin (pin 4) to VDD.
3.2 The Remote Loop Back Mode
When the XRT59L91 device is configured to operate in
the “Remote Loop-back” Mode, the XRT59L91 device
will ignore any signals that are input to the TxPOS and
TxNEG input pins. The XRT59L91 device will receive
the incoming line signals, via the RTIP and RRing input
pins. This data will be processed through the entire
Receive Section (within the XRT59L91) and will output
to the “Receive Terminal Equipment” via the
“RxPOS” and “RxNEG” output pins. Additionally, this
data will also be internally looped back to the “Transmit
Input Interface” block within the “Transmit Section”. At
this point, this data will be routed through the remainder
of the “Transmit Section” of the XRT59L91 device and
will be transmitted out onto the line via the “TTIP” and
“TRing” output pins.
Figure 13, illustrates the path that the data takes
(within the XRT59L91 device) when the chip is config-
ured to operate in the “Remote Loop-back” Mode.
RxLOS
R T IP
R R in g
RRe ceecieviev _e
EEq uqaulaizliezre _r
PPe aekakDDeteetcetcotro/r/
SSl i cl _iec re _r
L OL _{OS S}
DDe teetcetcotro _r
RReceecievieveOOutuptuptu _t
InItnetrefar _{fcaec e}
RxPOS
RxNEG
LLoop
L oL coacla _l
L oL oo po _{pB Ba} cakc _k
MMUUXX
Remote Loop Back
P a th
RRememo toete
L oL oo po _pBBa cakc _k
MMUUXX
RLoop
TTIP
T R in g
PPu lusleseSShahpaipnigng
CCirciruciut _it
TTrarnasnmsmit _iItnIpnuptut
InItnetrefrafcaec _e
TxPOS
TxNEG
TxClk
Figure 13. Illustration of the “Remote Loop-back” path, within the XRT59L91 Device
It should be noted that during “Remote Loop-back”
operation, any data which is input via the RTIP and
RRING input pins, will also be output to the Terminal
Equipment, via the RxPOS and RxNEG output pins.
Rev. P2.00
19