Datasheet

I2C
CLK1
CLK
0
Bit 0 to Bit 20
DS92LX2121, DS92LX2122
SNLS330I –MAY 2010–REVISED APRIL 2013 www.ti.com
FUNCTIONAL DESCRIPTION
The DS92LX2121 / DS92LX2122 Channel Link III chipset is intended for camera applications. The Serializer/
Deserializer chipset operates from a 10 MHz to 50 MHz pixel clock frequency. The DS92LX2121 transforms a
21-bit wide parallel LVCMOS data bus along with a bi-directional back channel control bus into a single high-
speed differential pair. The high speed serial bit stream contains an embedded clock and DC-balance information
which enhances signal quality to support AC coupling. The DS92LX2122 receives the single serial data stream
and converts it back into a 21-bit wide parallel data bus together with the back channel data bus.
The control channel function of the DS92LX2121 / DS92LX2122 provides bi-directional communication between
the image sensor and Electronic Control Unit (ECU). The integrated back channel transfers data bi-directionally
over the same differential pair used for video data interface. This interface offers advantages over other chipsets
by eliminating the need for additional wires for programming and control. The back channel bus is controlled via
an I
2
C port. The bi-directional back channel offers asymmetrical communication and is not dependent on video
blanking intervals.
DISPLAY APPLICATION
The DS92LX2121 / DS92LX2122 chipset is intended for interface between a host (graphics processor, FPGA,
etc.) and a Display. It supports a 21 bit parallel video bus for 18-bit color depth (RGB666) display format. In a
RGB666 configuration, 18 color bits (R [5:0], G[5:0], B[5:0]), Pixel Clock (PCLK) and three control bits (VS, HS
and DE) are supported across the serial link. The DS92LX2121 Serializer accepts a 21-bit parallel data bus
along with a bi-directional control bus. The parallel data and bi-directional control channel information is
converted into a single differential link. The integrated bi-directional control channel bus supports I
2
C compatible
operation for controlling auxiliary data transport to and from host processor and display module. The
DS92LX2122 Deserializer extracts the clock/control information from the incoming data stream and reconstructs
the 21-bit data with control channel data.
SERIAL FRAME FORMAT
The DS92LX2121 / DS92LX2122 chipset will transmit and receive a pixel of data in the following format:
Figure 23. Serial Bitstream for 28-bit Symbol
The High Speed Forward Channel is a 28-bit symbol composed of 21 bits of data containing video data & control
information transmitted from Serializer to Deserializer. CLK1 and CLK0 represent the embedded clock in the
serial stream. CLK1 is always HIGH and CLK0 is always LOW. This data payload is optimized for signal
transmission over an AC coupled link. Data is randomized, balanced and scrambled.
The bi-directional control channel data is transferred along with the high-speed forward data over the same serial
link. This architecture provides a full duplex low speed forward channel across the serial link together with a high
speed forward channel without the dependence of the video blanking phase.
DESCRIPTION OF BI-DIRECTIONAL CONTROL BUS AND I
2
C MODES
The I
2
C compatible interface allows programming of the DS92LX2121, DS92LX2122, or an external remote
device (such as a display) through the bi-directional control channel. Register programming transactions to/from
the DS92LX2121 / DS92LX2122 chipset are employed through the clock (SCL) and data (SDA) lines. These two
signals have open drain I/Os and both lines must be pulled-up to V
DDIO
by external resistor. Figure 5 shows the
timing relationships of the clock (SCL) and data (SDA) signals. Pull-up resistors or current sources are required
on the SCL and SDA busses to pull them high when they are not being driven low. A logic zero is transmitted by
driving the output low. A logic high is transmitted by releasing the output and allowing it to be pulled-up
externally. The appropriate pull-up resistor values will depend upon the total bus capacitance and operating
speed. The DS92LX2121 / DS92LX2122 I
2
C bus data rate supports up to 100 kbps according to I2C
specification.
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