Color Mapping And Terms - Emerson COM Express Carrier Design Manual

8.1.4 Color Mapping and Terms

FPD-Link and Open LDI Color Mapping
An LVDS stream consists of frames that pack seven data bits per LVDS frame. Details can be found in
the tables below. The LVDS clock is one seventh of the source-data clock. The order in which panel data
bits are packed into the LVDS stream is referred to as the LVDS color mapping. There are two LVDS
color mappings in common use: FPD-Link and Open LDI. Open LDI is the newer standard. The FPD-Link
and Open LDI standards are the same for panels with color depths of 18 bits (six red, six green, six blue)
or less. The 18 bits of color data and 3 bits of control data, or 21 bits total, are packed into three LVDS
data streams. The LVDS clock is carried on a separate channel for a total of four LVDS pairs–three data
pairs and a clock pair. For 24 bit color depths, a fourth LVDS data pair is required (for a total of five
LVDS pairs–four data and one clock). FPD-Link and Open LDI differ in this case. FPD-Link keeps the
least significant color bits on the original three LVDS data pairs and adds the most significant color bits
(the dominant or most important bits) to the fourth channel. Six bits are added: two red, two green,
and two blue (the seventh available bit slot in the fourth LVDS stream is not used).
A 24-bit, Open LDI implementation shifts the color bits on the original three LVDS data pairs up by two,
such that the most significant color bits for both 18 and 24-bit panels occupy the same LVDS slots. For
example, the most significant red color bit is R5 for 18-bit panels and R7 for 24- bit panels. The 18-bit
R5 and the 24-bit R7 occupy the same LVDS bit slot in Open LDI. The fourth LVDS data stream in Open
LDI carries the least significant bits of a 24-bit panel–R0, R1, G0, G1, B0, and B1. The advantage of
Open LDI is that it provides an easier upgrade and downgrade path than FPD-Link does. An 18-bit panel
can be used with an Open LDI 24-bit data stream by simply connecting the first three LVDS data pairs
to the panel, and leaving the fourth LVDS data pair unused. This does not work with FPD-Link because
the mapping for the 24-bit case is not compatible with the 18-bit case–the most significant data bits
are on the fourth LVDS data stream. If you design LVDS de-serializers, work around the module color
mapping by picking off the de-serializer outputs in the order needed. If you use a flat panel with an
integrated LVDS receiver, it is important that the display's color-mapping matches the module's color
mapping.
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Design Guide