DS90UH925Q-Q1 Datasheet, PDF (15/56 Pages) Texas Instruments – 720p 24-bit Color FPD-Link III Serializer with HDCP

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DS90UH925Q-Q1
SNLS336J – OCTOBER 2010 – REVISED NOVEMBER 2014
Feature Description (continued)
7.3.2 Low Speed Back Channel Data Transfer
The Low-Speed Backward Channel (LS_BC) of the DS90UH925Q-Q1 provides bidirectional communication
between the display and host processor. The information is carried back from the Deserializer to the Serializer
per serial symbol. The back channel control data is transferred over the single serial link along with the high-
speed forward data, DC balance coding and embedded clock information. This architecture provides a backward
path across the serial link together with a high speed forward channel. The back channel contains the I2C,
HDCP, CRC and 4 bits of standard GPIO information with 10 Mbps line rate.
7.3.3 Backward Compatible Mode
The DS90UH925Q-Q1 is also backward compatible to DS90UR906Q and DS90UR908Q FPD Link II
deserializers at 5-65 MHz of PCLK. It transmits 28-bits of data over a single serial FPD-Link II pair operating at
the line rate of 140 Mbps to 1.82 Gbps. The backward configuration mode can be set via MODE_SEL pin
(Table 4) or the configuration register (Table 6). Note: frequency range = 15 - 65MHz when LFMODE = 0 and
frequency range = 5 - <15MHz when LFMODE = 1.
7.3.4 Common Mode Filter Pin (CMF)
The serializer provides access to the center tap of the internal termination. A capacitor must be placed on this pin
for additional common-mode filtering of the differential pair. This can be useful in high noise environments for
additional noise rejection capability. A 0.1 μF capacitor must be connected to this pin to Ground.
7.3.5 Video Control Signal Filter
When operating the devices in Normal Mode, the Video Control Signals (DE, HS, VS) have the following
restrictions:
• Normal Mode with Control Signal Filter Enabled: DE and HS — Only 2 transitions per 130 clock cycles are
transmitted, the transition pulse must be 3 PCLK or longer.
• Normal Mode with Control Signal Filter Disabled: DE and HS — Only 2 transitions per 130 clock cycles are
transmitted, no restriction on minimum transition pulse.
• VS — Only 1 transition per 130 clock cycles are transmitted, minimum pulse width is 130 clock cycles.
Video Control Signals are defined as low frequency signals with limited transitions. Glitches of a control signal
can cause a visual display error. This feature allows for the chipset to validate and filter out any high frequency
noise on the control signals. See Figure 12.
PCLK
IN
HS/VS/DE
IN
Latency
PCLK
OUT
HS/VS/DE
OUT
Pulses 1 or 2
PCLKs wide
Filetered OUT
Figure 12. Video Control Signal Filter Waveform
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