
HDCP Gigabit Multimedia Serial Link
Serializer with LVDS System Interface
MAX9265
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As shown in Figure 21, the remote-side device converts the
packets going to or coming from the peripherals from the
UART format to the I2C format and vice versa. The remote
device removes the byte number count and adds or receives
the ACK between the data bytes of I2C. The I2C’s data rate is
the same as the UART data rate.
Interfacing Command-Byte-Only I2C Devices
The serializer and GMSL deserializer UART-to-I2C conver-
sion interfaces with devices that do not require register
addresses, such as the MAX7324 GPIO expander. In this
mode, the I2C master ignores the register address byte and
directly reads/writes the subsequent data bytes (Figure 22).
Change the communication method of the I2C master using
the I2CMETHOD bit. I2CMETHOD = 1 sets command-byte-
only mode, while I2CMETHOD = 0 sets normal mode where
the first byte in the data stream is the register address.
Bypass Mode
In bypass mode, the serializer/GMSL deserializer ignore
UART commands from the FC and the FC communi-
cates with the peripherals directly using its own defined
UART protocol. The FC cannot access the serializer/GMSL
deserializer’s registers in this mode. Peripherals accessed
through the forward control channel using the UART
interface need to handle at least one RXCLKIN_ period
±10ns of jitter due to the asynchronous sampling of the
UART signal by RXCLKIN_. Set MS = high to put the control
channel into bypass mode. For applications with the FC
connected to the deserializer (CDS is high), there is a 1ms
wait time between setting MS high and the bypass control
channel being active. There is no delay time in switching
to bypass mode when the FC is connected to the serial-
izer (CDS = low). Bypass mode accepts bit rates down to
9.6kbps in either direction. See the Interrupt Control section
for interrupt functionality limitations. The control-channel
data pattern should not be held low longer than 100Fs
in either base or bypass mode to ensure proper interrupt
functionality.
Interrupt Control
The INT pin of the serializer is the interrupt output and the
INT pin of the GMSL deserializer is the interrupt input. The
interrupt output on the serializer follows the transitions at the
interrupt input. This interrupt function supports remote-side
functions such as touch-screen peripherals, remote power-
up, or remote monitoring. Interrupts that occur during
periods where the reverse control channel is disabled, such
as link startup/shutdown, are automatically resent once the
reverse control channel becomes available again. Bit D4
of register 0x06 in the GMSL deserializer also stores the
interrupt input state. The INT output of the serializer is low
after power-up. In addition, the FC can set the INT output of
the serializer by writing to the SETINT register bit. In normal
operation, the state of the interrupt output changes when
the interrupt input on the GMSL deserializer toggles. Do not
send a logic-low value longer than 100Fs in either base or
bypass mode to ensure proper interrupt functionality.
Pre/Deemphasis Driver
The serial line driver in the serializer employs current-mode
logic (CML) signaling. The driver can generate an adjust-
able preemphasized waveform according to the cable
length and characteristics. There are 13 preemphasis set-
tings as shown in Table 5. Negative preemphasis levels are
deemphasis levels in which the preemphasized swing level
is the same as normal swing, but the no-transition data is
deemphasized. Program the preemphasis levels through
register 0x05 D[3:0] of the serializer. 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, the serializer supports spread spectrum. Turning
on spread spectrum on the serializer spreads the serial
link, which is tracked by the serializer deserializer. The
six selectable spread-spectrum rates at the serial output
are Q0.5%, Q1%, Q1.5%, Q2%, Q3%, and Q4% (Table 6).
Some spread-spectrum rates can only be used at lower
RXCLKIN_ frequencies (Table 7). There is no RXCLKIN_
frequency limit for the 0.5% spread rate.
Set the serializer’s 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 serializer’s 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 serializer or
GMSL deserializer does not affect the audio data stream.
The serializer includes a sawtooth divider to control the
spread-modulation rate. Autodetection or manual pro-
gramming of the RXCLKIN_ 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 modu-
lation frequency according to the RXCLKIN_ frequency.
Always keep the modulation frequency between 20kHz to
40kHz to ensure proper operation.