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8/16 bit mode

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  • 8/16 bit mode

    I have the 4DLCD-32qa Display.
    The manual shows pin 3 IMO(8/16) is 1=8bit and 0=16bit mode.

    Regarding the 8bit mode: the ILI9341 has multiple 8bit modes ?
    which one is it ?

    The pin RS of the display, is that the D/CX pin of the ILI9341 ?

    Is there a schematic where I can see how the display pins are connected to the ILI9341 ?

    Last edited by harry4516; 24 March 2016, 08:56 PM.

  • #2
    The 8/16 bit hardware select pin is for the hardware interface only. It is completely separate to the 'software'(register adjusted) modes.

    It generally only refers to the transfer of colours over the databus, in 8 bit mode the colours are transferred as 2 8 bit transfers, in 16 bit mode colours are transferred as 1 16 bit transfer.

    RS (Register Select) is the same as D/C (Data/Control i.e. Register Select)

    No, I don't believe there is a schematic.


    • #3
      thank you for answering Mark,

      I tried to use the 8-bit hardware mode IMO(8/16) to Vcc. But the data lines DB0-7 of the display are disabled.
      Then I switched to 16-bit hardware mode IMO to GND, and this works fine without any problems.

      I would prefer the 8bit mode because I don't have so many GPIOs. But in 8-bit the DB0 to DB7 lines of the display are doing nothing, just tristate.

      Thats why I'm asking. The ILI9341 supports several 8bit modes selected by IM0 to IM3 pins, which are not available at the connector.
      The IMO pin-3 is probably connected to IM0-3 in some way, but how is that done ?
      Which hardware mode of the ILI9341 is selected when IMO is connected to Vcc ?



      • #4
        Ah, right, I see what you are saying now.

        Sorry I don't know and the person who might has started his Easter break, so it will take a few days to get the answer.


        • #5
          Hi Harry4516

          Sorry for the delay, I was away for the Easter break.

          So the 4DLCD-32QA uses the ILI9341V, and to configure it for 16bit mode you pull IM0 to GND (0) and its then the full databus of DB0 to DB15
          For 8bit more, you pull IM0 to VCC (1) and its then the upper half of the databus DB8 to DB15

          I hope that helps


          • #6
            Hi James,

            thank you for your explanation, so its D8-15 which is the 8080 mode II. Thats fine I can use it now.

            Maybe you want to write a note into the manual.



            • #7
              Dear 4D Support Team,

              I tried to connect also a 4DLCD-32QA display to an AtXMega, using 8 bit mode - but without any success.

              I intend to use this display for a series of products in future because it fully fits my needs in a small touch display. All I need is to get the basics working, so I can later add a graphical libary to realize product features.

              My first test scenario was to power the chip, pulling reset line for 10ms, release it, waiting then for 120ms before starting a "Read display identification information (04h)" where I assume to read ID1,2 and 3 with values not zero.

              I first started assuming 8080 mode 0 (IM3 set to GND internally) - this mode also offers 8/16 bit select capability using the IM0 pin.
              Within documentation the true mode is not refered - same for several ILI-Pins, so one can just assume ...

              Can you confirm it is really 8080 mode II which is selected within this display? (IM3 is pulled high, IM0 is brought outside via pin, so user may switch between 8 and 16 bit mode?)
              According to the Datasheet, Data lines DB10-DB17 shall be used when being in 8080 mode II - and DB lines 0-15 are available on pins only. This would explain why the given command is not answered - but there must be something else..

              When reading the previous posts here I thought this could be the error - but using D8-D15 for data failed...

              Actually I only got zeros read out - and wondered why. using a wrong data line for cmd 04 could be one reason.
              The display itself seems to at least partially react to rd strobe signals: in one experiment I used a 10K pullup resistor on one data line - and I saw that on positive edge of rd signal, the level is shortly pulled down.
              So at least power supply of logical part, CS and WR shall be working so far..

              Do you have any Ideas what could cause the command to not respond any "meaningful" values ? (by the way which values are meaningful? - didn't find any values in the 32QA datasheet for
              LCD module’s manufacturer ID.
              LCD module/driver version ID.
              LCD module/driver ID.

              I would be very thankful if you could help me tracking down and solving the problem I have, so any help you or other users can give would be greatly appreciated.
              If it helps, I could give oscilloscope screenshots and exact pinout usuage - maybe there was some kind of pinout errors within documentation 4DLCD-32QA V1.0 ?
              Unfortunately I wasn't able to find any newer version like this.

              Thank you VERY MUCH in advance


              • #8
                To clarify further IM1=0, IM2=0, IM3=3.3v.

                So D8 to D15 should work just fine as internally they are connected to DB10-17

                Click image for larger version

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