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

• Manufacturer Part Number: FPDXSDUR-43USB/NOPB
• Description: KIT EVAL DS99R421 CONV TO LVDS
• Manufacturer: National Semiconductor

Specifications of FPDXSDUR-43USB/NOPB

• Main Purpose: Interface, Serializer, Deserializer (SERDES)
• Utilized Ic / Part: DS90UR124, DS99R421
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Other names: FPDXSDUR-43USB

Table 2.
JP6,VR1: Pre-Emphasis Feature Selection
Reference
JP6
JP6 &
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 R5 on the DS99R421 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)
JP6 MUST have a jumper to
use VR1 potentiometer.
VR1 = 0Ω to 20KΩ,
JP6 + 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
Ω
Description
fixed resistor plus ~20K
> 6KΩ
PRE
)] x 40,
Ω
National Semiconductor Corporation
value is based
(
R6) =
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: 5/12/2008
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