
MAX9272
28-Bit GMSL Deserializer for Coax or STP Cable
31
Maxim Integrated
PRBS Test
The serializer includes a PRBS pattern generator that
works with bit-error verification in the deserializer. To run
the PRBS test, set PRBSEN = 1 (0x04, D5) in the deserial-
izer and then in the serializer. To exit the PRBS test, set
PRBSEN = 0 (0x04, D5) in the serializer.
Line Equalizer
The deserializer includes an adjustable line equalizer to
further compensate cable attenuation at high frequen-
cies. The cable equalizer has 11 selectable levels of
compensation from 2.1dB to 13dB (
Table 5). The device
powers up with the equalizer disabled. To select other
equalization levels, set the corresponding register bits
in the deserializer (0x05 D[3:0]). Use equalization in the
deserializer, together with preemphasis in the serializer,
to create the most reliable link for a given cable.
Spread Spectrum
To reduce the EMI generated by transitions, the dese-
rializer output is programmable for spread spectrum. If
the serializer driving the deserializer has programmable
spread spectrum, do not enable spread for both at the
same time or their interaction will cancel benefits. The
programmable spread-spectrum amplitudes are Q2%
The deserializer includes a sawtooth divider to
control the spread-modulation rate. Autodetection of
the PCLKOUT operation range guarantees a spread-
spectrum modulation frequency within 20kHz to 40kHz.
Additionally, manual configuration of the sawtooth divider
(SDIV: 0x03, D[5:0]) allows the user to set a modulation
frequency according to the PCLKOUT frequency. When
ranges are manually selected, program the SDIV value
for a fixed modulation frequency around 20kHz.
Manual Programming
of the Spread-Spectrum Divider
The modulation rate for the deserializer relates to the
PCLKOUT frequency as follows:
(
) PCLKOUT
M
f
1 DRS
MOD SDIV
= +
×
where:
fM = Modulation frequency
DRS = DRS value (0 or 1)
fPCLKOUT = PCLKOUT frequency
MOD = Modulation coefficient given in
Table 7SDIV = 5-bit SDIV setting, manually programmed by
the FC
To program the SDIV setting, first look up the modula-
tion coefficient according to the desired bus-width and
spread-spectrum settings. Solve the above equation for
SDIV using the desired pixel clock and modulation fre-
quencies. If the calculated SDIV value is larger than the
maximum allowed SDIV value in
Table 7, set SDIV to the
maximum value.
Table 5. Cable Equalizer Boost Levels
Table 6. Parallel Output Spread
Table 7. Modulation Coefficients and
Maximum SDIV Settings
*The equalizer is disabled at power-up.
BOOST SETTING
(0x05 D[3:0])
TYPICAL BOOST GAIN
(dB)
0000
2.1
0001
2.8
0010
3.4
0011
4.2
0100
5.2
0101
6.2
0110
7
0111
8.2
1000
9.4
1001
10.7
Default*
1010
11.7
1011
13
SS
SPREAD (%)
00
No spread spectrum. Power-up default.
01
Q
2% spread spectrum.
10
No spread spectrum.
11
Q
4% spread spectrum.
SPREAD-
SPECTRUM
SETTING (%)
MODULATION
COEFFICIENT
(dec)
SDIV UPPER
LIMIT (dec)
4
208
15
2
208
30