SERDESUR-43USB/NOPB National Semiconductor, SERDESUR-43USB/NOPB Datasheet - Page 9

• Manufacturer Part Number: SERDESUR-43USB/NOPB
• Description: BOARD EVAL DS90UR124,DS90UR241
• Manufacturer: National Semiconductor

Specifications of SERDESUR-43USB/NOPB

• Main Purpose: Interface, Serializer, Deserializer (SERDES)
• Utilized Ic / Part: DS90UR241, DS90UR124
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Other names: SERDESUR-43USB

JP3,VR1: Pre-Emphasis Feature Selection
Reference
JP3
JP3 &
VR1
Pre-emphasis user note:
Pre-emphasis must be adjusted correctly based on application frequency, cable
quality, cable length, and connector quality. Maximum pre-emphasis should only
be used under extreme worse case conditions; for example at the upper
frequency specification of the part and/or low grade cables at maximum cable
lengths. Typically all that is needed is minimum pre-emphasis. Users should
start with no pre-emphasis first and gradually apply pre-emphasis until there is
clock lock and no data errors. The best way to monitor the pre-emphasis effect is
to hook up a differential probe to the 100Ω termination resistor (R1) on the
DS90UR124 Rx demo board (NOT to R27 on the DS90UR241 Tx demo board). The
reason for monitoring R1 on the Rx side is because you want to see what the
receiver will see the attenuation signal AFTER the cable/connector.
Pre-Emphasis – helps to
increase the eye pattern
opening in the LVDS stream
Pre-Emphasis adjustment
(via screw)
JP1 MUST have a jumper to
use VR1 potentiometer.
VR1 = 0Ω to 20KΩ,
JP1 + VR1 + 6KΩ
~6KΩ (maximum pre-
emphasis) to
~26KΩ (minimum pre-
emphasis*).
I
R
*Note: maximum is based on resistor
value. In this case ~26K
on the ~6k
maximum potentiometer value. User can
use hundreds of Kohms to reduce the pre-
emphasis value.
PRE
PRE (minimum)
= [1.2/(R
SERDES Evaluation Kit DS90UR241/124 USB Version 0.1 User Manual
Ω
Description
fixed resistor plus ~20K
> 6KΩ
PRE
)] x 40,
Ω
National Semiconductor Corporation
value is based
(
R26) =
Ω
Disabled –
no jumper
(Default)
Clockwise
increases
R
which
decreases
pre-
emphasis
PRE
(floating)
OPEN
value
Enabled –
With jumper
Counter-
Clockwise
decreases
R
which
increases
pre-
emphasis
(Path to GND)
PRE
CLOSED
value
Date: 5/8/2008
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