COMPRO X800 - START UP GUIDE Especificaciones descargar pdf (Pagina 23)

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MAX9249

Gigabit Multimedia Serial Link

Serializer with LVDS System Interface

*Negative preemphasis levels denote deemphasis.

Preemphasis Driver

The serial line driver in the MAX9249 employs cur-

rent-mode logic (CML) signaling. The driver can be

programmed to generate a preemphasized waveform

according to the cable length and characteristics. There

are 13 preemphasis settings, as shown in Table 4.

Negative preemphasis levels are deemphasis levels in

which the swing is the same as normal, but the no-tran-

sition data is deemphasized. Program the preemphasis

levels through register 0x05 D[3:0] of the MAX9249. This

preemphasis function compensates the high-frequency

loss of the cable and enables reliable transmission over

longer link distances. Additionally, a lower power-drive

mode can be entered by programming CMLLVL bits

(0x05 D[5:4]) to reduce the driver strength down to

75% (CMLLVL = 10) or 50% (CMLLVL = 01) from 100%

(CMLLVL = 11, default).

Spread Spectrum

To reduce the EMI generated by the transitions on the

serial link and outputs of the GMSL deserializer, both

the MAX9249 and GMSL deserializer support spread

spectrum. Turning on spread spectrum on the MAX9249

spreads the serial data and the GMSL deserializer out-

puts. Do not enable spread for both the MAX9249 and

GMSL deserializer. The six selectable spread-spectrum

rates at the MAX9249 serial output are ±0.5%, ±1%,

±1.5%, ±2%, ±3%, and ±4% (Table 5). Some spread-

spectrum rates can only be used at lower RXCLKIN_

frequencies (Table 6). There is no RXCLKIN_ frequency

limit for the 0.5% spread rate.

Set the MAX9249 SSEN input high to select 0.5% spread

at power-up and SSEN input low to select no spread at

power-up. The state of SSEN is latched upon power-up

or when resuming from power-down mode. Whenever

the MAX9249 spread spectrum is turned on or off, the

serial link automatically restarts and remains unavailable

while the GMSL deserializer relocks to the serial data.

Turning on spread spectrum on the MAX9249 or GMSL

deserializer does not affect the audio data stream.

Changes in the MAX9249 spread settings only affect

the GMSL deserializer MCLK output if it is derived from

RXCLKIN_ (MCLKSRC = 0).

Table 4. CML Driver Strength (Default Level, CMLLVL = 11)

Table 5. Serial Output Spread

PREEMPHASIS LEVEL

(dB)*

PREEMPHASIS

SETTING

(0x05, D[3:0])

CML

(mA)

PRE

(mA)

SINGLE-ENDED VOLTAGE SWING

MAX

(mV)

MIN

(mV)

-6.0 0100 12 4 400 200

-4.1 0011 13 3 400 250

-2.5 0010 14 2 400 300

-1.2 0001 15 1 400 350

0 0000 16 0 400 400

1.1 1000 16 1 425 375

2.2 1001 16 2 450 350

3.3 1010 16 3 475 325

4.4 1011 16 4 500 300

6.0 1100 15 5 500 250

8.0 1101 14 6 500 200

10.5 1110 13 7 500 150

14.0 1111 12 8 500 100

SS SPREAD (%)

000

No spread spectrum.

Power-up default when SSEN = low.

001

Q0.5% spread spectrum.

Power-up default when SSEN = high.

010

Q1.5% spread spectrum

011

Q2% spread spectrum

100 No spread spectrum

101

Q1% spread spectrum

110

Q3% spread spectrum

111

Q4% spread spectrum

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 35 36

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