Kontron COMe Starterkit Eval T2 - Manual (Page 93)

COM Express Interfaces
2.11.1.4. 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 (6
Red, 6 Green, 6 Blue) or less. The 18 bits of color data and 3 bits of control data, or 21 bits total,
are packed into 3 LVDS data streams. The LVDS clock is carried on a separate channel for a
total of 4 LVDS pairs – 3 data pairs and a clock pair.
For 24-bit color depths, a 4th LVDS data pair is required (for a total of 5 LVDS pairs – 4 data and
1 clock). FPD-Link and Open LDI differ in this case. FPD-Link keeps the least significant color
bits on the original 3 LVDS data pairs and adds the most significant color bits (the dominant or
“most important” bits) to the 4th channel. Six bits are added: 2 Red, 2 Green, and 2 Blue (the
seventh available bit slot in the 4th LVDS stream is not used).
A 24-bit, Open LDI implementation shifts the color bits on the original 3 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 4th
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 1st three LVDS data pairs to the panel, and leaving the 4th 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 4th LVDS data stream.
If you design LVDS deserializers, work around the Module color-mapping by picking off the
deserializer outputs in the order needed. If you use a flat panel with an integrated LVDS receiver,
it is important that the displays color-mapping matches the Module’s color-mapping.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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