MAX96708 datasheet(29/68 Pages) MAXIM

29 / 68 page

Control Channel and Register Programming

The control channel sends I2C or UART information

across the serial link for control of the serializer, deserial-

izer, and any attached peripherals. The control channel

is multiplexed onto the serial link and is available with or

without the video channel.

Forward Control Channel

Control data sent from the serializer to the deserializer is

sent on the forward control channel. The data is encoded

as one of the serial bits in the forward high-speed link.

After deserialization, the forward control-channel data is

extracted from the serial link. The forward control-channel

bandwidth exceeds the maximum external control data

rate, and all data sent on the forward control channel

appears on the remote side after transmission delay of a

few bit times.

Reverse Control Channel

Control data sent from the deserializer to the serializer is

sent on the reverse control channel. The data is encoded

as a series of 1μs pulses, with a maximum raw data rate of

1Mbps. High-immunity mode is available to increase the

robustness of the reverse control channel at a reduced

raw bit rate of 500kbps (Table 1). Setting the REV_FAST

bit = 1 increases this rate back to 1Mbps. In I2C mode,

when the input data rate (after encoding) exceeds the

reverse data rate, the input clock is held through clock

stretching to slow the external clock to match the internal

bit rate.

UART Interface

The UART interface, compatible with all GMSL devices,

sends commands from device to device through several

UART packets. Set I2CSEL = 0 to set the device to use

UART protocol.

I2C Interface

The serial link connects the serializer and deserializer I2C

interfaces together through the control channel. When an

I2C master sends a command to one side of the link (local

side) the control channel forwards this information to and

from the other side of the link (remote side), allowing a

single microcontroller to configure the serializer,

deserializer, and peripherals. The microcontroller can be

located on the serializer side (display applications) and the

deserializer side (camera applications). Dual-μC opera-

tions are supported as long as a software-arbitration

method is used. The serial link assumes that only one

microcontroller is talking at any given time.

Remote-End Operation

When an I2C master initiates communication on the local

slave device (the serializer/deserializer directly connected

to the master), the remote-side device acts as a master

device that sends data forwarded from the local-side

device, and forwards any data received from peripher-

als attached to the remote-side device. This remote-side

master device operates according to the timing settings in

the I2C Master setting register. Set the master settings to

match the timing settings used by the external microcon-

troller.

Clock-Stretch Timing

The I2C interface uses clock stretching to allow time for

data to be forwarded across the serial link. The master

microcontroller, along with any attached peripherals, must

accept clock stretching of the GMSL devices.

GPO/GPI Control

GPO on the serializer follows GPI transitions on the

deserializer. This GPO/GPI function can be used to

transmit signals such as a frame sync in a surround-view

camera system (see the Providing a Frame Sync (Camera

Applications) section).

HIM PIN SETTING

REVFAST BIT

REVERSE CONTROL-

CHANNEL MODE

MAX UART/I2C BIT RATE

(kbps)

Low

Legacy reverse control-

channel mode (compatible with

all GMSL devices)

1000

High

High-immunity mode

500

Fast high-immunity mode

(requires serial-data rate >

1.25Gbps)

1000

Table 1. Reverse Control-Channel Modes

X = Don’t care.

www.maximintegrated.com

Maxim Integrated │ 29

MAX96708

14-Bit GMSL Deserializer

with Coax or STP Cable Input

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