SP3508EB Datasheet, PDF (32/36 Pages) Sipex Corporation – Evaluation Board Manual

TERM_OFF FUNCTION
The SP3508 contains a TERM_OFF pin that
disables all three receiver input termination
networks regardless of mode. This allows
the device to be used in monitor mode ap-
plications typically found in networking test
equipment.
The TERM_OFF pin internally contains a
pull-down device with an impedance of over
500kΩ, which will default in a "ON" condition
during power-up if V.35 receivers enable
line and the SHUTDOWN mode from the
decoder will disable the termination regard-
less of TERM_OFF.
LOOPBACK FUNCTION
The SP3508 contains a LOOPBACK pin that
invokes a loopback path. This loopback path
is illustrated in Figure 50. LOOPBACK has
an internal pull-up resistor that defaults to
normal mode during power up or if the pin is
left floating. During loopback, the driver out-
put and receiver input characteristics will still
adhere to its appropriate specifications.
FEATURES
There are internal pull-up devices on D0,
D1 and D2, which allow the device to be in
SHUTDOWN mode ("111") upon power up.
However, if the device is powered-up with
the D_LATCH at a logic HIGH, the decoder
state of the SP3508 will be undefined.
CTR1/CTR2 EUROPEAN COMPLIANCY
As with all of Exar's previous multi-protocol
serial transceiver IC's the drivers and re-
ceivers have been designed to meet all the
requirements to NET1/NET2 and TBR2 in
order to meet CTR1/CTR2 compliancy. The
SP3508 is also tested in-house at Exar and
adheres to all the NET1/2 physical layer
testing and the ITU Series V specifications
before shipment. Please note that although
the SP3508, as with its predecessors, ad-
here to CRT1/CTR2 compliancy testing,
any complex or usual configuration should
be double-checked to ensure CTR1/CTR2
compliance. Consult the factory for details.
DECODER AND D_LATCH FUNCTION
The SP3508 contains a D_LATCH pin that
latches the data into the D0, D1 and D2
decoder inputs. If tied to a logic LOW ("0"),
the latch is transparent, allowing the data at
the decoder inputs to propagate through and
program the SP3508 accordingly. If tied to a
logic HIGH ("1"), the latch locks out the data
and prevents the mode from changing until
this pin is brought to a logic LOW.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com

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