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Do you have a question on Embedded electronics and controls? Ask our Expert, Paul Clarke

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Paul Clarke

Paul has 20+ years of working as a digital electronics engineer and has strong software skills in assembly and C for embedded systems. Currently developing embedded electronics for thermal management control solutions for the air movement industry (HVAC & RAC).




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  • Hi Paul,

    Hope I am asking the right person....

    I have been toying with the idea of an LCD project, and one part involves multiple small 1.5" LCD's.  These LCD's have been taken from those Photo Key Chains you all see, and they use an 8 bit parallel data bus (hope I am saying this correct).  Also each LCD driver has a CS (Chip select).

    So here is what I want to do.....Have 5,10 or even more of these LCD's essentially all connected to a 8 bit serial BUS, each LCD would have its own CS line so I can write individually to each LCD.

    First question - Is this possible?

    Second question - Is there a limit to the number of LCD's I can connect to the BUS?  What are the potential limits and how would I overcome them?

     

    Hope this is all clear.

     

    Thanks

    Mark

Reply

  • Hi Paul,

    Hope I am asking the right person....

    I have been toying with the idea of an LCD project, and one part involves multiple small 1.5" LCD's.  These LCD's have been taken from those Photo Key Chains you all see, and they use an 8 bit parallel data bus (hope I am saying this correct).  Also each LCD driver has a CS (Chip select).

    So here is what I want to do.....Have 5,10 or even more of these LCD's essentially all connected to a 8 bit serial BUS, each LCD would have its own CS line so I can write individually to each LCD.

    First question - Is this possible?

    Second question - Is there a limit to the number of LCD's I can connect to the BUS?  What are the potential limits and how would I overcome them?

     

    Hope this is all clear.

     

    Thanks

    Mark

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  • in reply to winneymj

    @winneymj

     

    The limit is time and possibly chip (display) select lines.  All the 8 bit parallel data lines would be in parallel to all the displays, and the chip selects would fire sequentially to each display in turn allowing the 8-bit data to be written.  So the question turns into how fast can you write to each display so that it looks visually smooth and how many I/O do you have to do 8 data lines plus X-Chip Selects.

     

     

    http://en.wikipedia.org/wiki/Multiplexing

  • in reply to winneymj

    You need to tell us more about the LCD displays and what you are trying to do with them. There is also a bit of confusion in your 3 rd paragraph when you say "connected to a 8 bit serial bus" - I think you mean parallel.

     

    The LCD chips will probably have some control lines as well as CS and data  -we need to know about them and we need to know what you are thinking of using to drive them all.

     

    The more devices you connect in parallel the slower the data transfers will be and the more data integrity problems you will have. These problems will get worse if the phyiscal distance between displays is large.

     

    But there are solutions to drive any number of displays ......

     

    Michael Kellett