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AM1808 LCD Controller Interface for 8 Bit RGB Mode

Gloria Mattson
Prodigy 80 points
Other Parts Discussed in Thread: AM1808

I would like to interface the AM1808 LCD controller to a 320(RGB) x 240 LCD using an 8 Bit Mode.  In the normal 24 bit mode, we would send 8 bits of red, 8 bits of green and 8 bits of blue all in one clock cycle at ~6.4Mhz.  In the desired 8 bit mode, we would go 27MHz and send 8 bits of red with one clock, 8 bits of green with the second clock, and 8 bits of blue with the 3rd clock.

I wanted some input on the feasibility of the 8 bit mode interface, how to setup this mode and which 8 bits of the AM1808 interface to use.

Timing diagram from the LCD datasheet describing the 8-bit mode.

  • 0
    TI__Mastermind 27585 points

    The mode you are referring to is called Serial RGB or TDM mode. The AM1808 only supports Parallel RGB565, so there is not a way for the LCD controller to do this natively.

    The DM35x, DM36x, OMAP35xx devices, however, do support Serial RGB mode which would work with the LCD you referred to.

    Jeff

  • 0 in reply to jc-ti
    Prodigy 30 points

    But can't you just put the LCD controller into an "8-Bit per pixel monochrome" type mode, and software just has to know that it takes "three 8-bit pixels" to make up a single RGB pixel as seen on the display? 

  • 0 in reply to David Kessner
    TI__Mastermind 27585 points

    Is your panel an active or passive LCD panel? For active mode, it will always output in 16 bit RGB. You can of course always structure the frame buffer in such a way that the D[7:0] outputs the desired value, but that would require extra memory in the frame buffer for the unused bits.

    Jeff

  • 0 in reply to jc-ti
    Genius 3685 points

    Hi Jeff,

    While I agree that it will waste memory (like 225KB for a QVGA 24-bit display, which of cause can be measured, but most likely not will be critical compared to a normal system memory of several Megabytes? :-) I think the bigger issue will be that all frame buffer related software will have to be updated to support this "new" format of having an interleaved dummy byte. This is of cause possible, but might be a bigger or smaller task dependent on which kind of graphics routines/libraries Gloria/David expect to use...

    But as said - Nothing which can't be handled in case wanted/needed :-)

    Best regards - Good luck
      Søren