Datasheet

IDLE
LINK
DETECT
LINK
ACQUISITION
NORMAL
TxCLKIN exist
Link Detect
fail
TxCLKIN does
not exist
Power-On/Reset
RS: 1, DC_B: 0
RS: 1, DC_B: 1
DS32EL0421, DS32ELX0421
www.ti.com SNLS282F –MAY 2008–REVISED APRIL 2013
Figure 7. Serializer State Diagram
SCRAMBLER and NRZI Encoder
The CDR of the DS32EL0124 and the DS32ELX0124 expect a transition density of 20% for a period of 200 μs. If
the scrambler and NRZI encoder are enabled, the raw or DC-balanced serialized data is scrambled to improve
transition density. The scrambler accepts 20 bits of data and encodes it using the polynomial X
9
+ X
4
+ 1. The
data can then be sent to the NRZ-to-NRZI converter before being output.
Enabling the scrambler can help to lower EMI emissions by spreading the spectrum of the data. Scrambling also
creates transitions for the deserializer’s CDR to properly lock onto.
The scrambler and NRZI encoder are enabled or disabled by default depending on how the DC_B and RS pins
are configured. To override the default scrambler setting two register writes must be performed. First, write to
register 22’h and set bit 3 to unlock the scrambler register. Next write to register 21’h and change bit 4 to the
desired value. The NRZI encoder can be enabled or disabled independently of the scrambler by controlling bit 7
of register 21'h and bit 4 of register 22'h.
CML OUTPUT DATA INTERFACING
The serial outputs provide low-skew differential signals. Internal resistors connected from TxOUTn+ and
TxOUTn- to VDD25 terminate the outputs. The output level can be programmed by adjusting the pull-down
resistor to the VOD_CTRL pin. The output terminations can also be programmed to be either 50 Ω or 75 Ω.
The output buffer consists of a current mode logic (CML) driver with user configurable de-emphasis control,
which can be used to optimize performance over a wide range of transmission line lengths and attenuation
distortions resulting from low cost CAT(-5, -6, -7) cable or FR–4 backplane. Output de-emphasis is user
programmable through either device pins DE_EMPH0 and DE_EMPH1 or SMBus interface. Users can control
the strength of the de-emphasis to optimize for a specific system environment. Please see Table 1 for details.
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