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

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.

Copyright © 2008–2013, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: DS32EL0421 DS32ELX0421