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Linux/ADS7845: Linux/ADS7845: It can't work and what is problem?

Part Number: ADS7845

Tool/software: Linux

Hi team,

My customer used ADS7845 for five wire touch screen.

Below is SCH.

1. R73 and C101 has remove and AUXIN connect to GND,  

2 .R357-R361 has remove. R66,R68,R69,R71,R349 = 0R。

Linux driver :

We run the system and find we touch the screen like below picture showing the direction. And the X Y data change small, like ADS7845 didn't work.

Do you know why? Thanks!

  • Hello Eggsy,

    We're reviewing the SCH and other information but are having trouble understanding the last image and what the comments around the arrows means? 

    Please note that we do not provide Linux driver support for the TSC devices.  We will review summaries of the data collected (like you've provided) along with schematics, layouts, and digital communication captures to help debug customer designs.

  • Hi Collin,

    There are three comments around the arrows and they means:

    i" touch the screen from left to right" , 

    " touch the screen from up to rdown" 

    and " touch the screen from right to left" .

    And the screen show the data is mean the value X, Y , touch or not. 

    The linux driver is used by

    Do you have any suggestions?

    Is the SCH no problem and what else we should provide ?


  • Hello Eggsy,

    The schematic you provided looks good to me but I just have a couple of questions. 

    1. What is the resolution of the touch screen? From your screenshots, I see 1024 x 768. Is this correct? If so, this resolution is well within the range of the ADS7845.

    2. Is the device in 12-bit mode? It looks like it but just a sanity check.

    3. In the first image, x-max is set to 8000 and y-max is set to 4800. Is this supposed to be the resolution of the ADS7845? If so, the resolution in 12-bit mode is 4096 x 4096.



  • Hello Eggsy,

    It has been approximately 5 days since we last heard from you and I am under the impression that the issue was resolved so I will be marking the post as "TI Thinks Resolved". 

    If the issue is still there or if you have another question, feel free to follow-up. 



  • Hi Aaron,

    The screen is 1024 x 768 and set ADC to 12-bit mode.

    Do you have any suggestions and good way to give us to try?


  • Hi Eggsy,

    Can you clarify why x-max is set to 8000?

    Also, if the customer hasn't done so already, it may be a good idea to go through the Touch Screen Controller Tips document. There is some useful information in there regarding touch screen controllers.


  • Hi Aaron,

    I have set X-max and Y-max to 4096*4096 or 1024*768.But it still does not work.

    I saw the printy info " "external vREF for ADS7845 not spectified."  when linux start, like below pic.


    And I add below info "ti,vref-mv = <&reg_3p3v>;" into device tree, like below pic. But it still printy  "external vREF for ADS7845 not spectified."

    Do you have any suggestions? Thanks!

  • Hi Eggsy,

    Unfortunately we do not offer full driver support but I can recommend some things...

    1. It seems that the reference voltage is supposed to be defined in mV. can you look into this?

    2. Have you probed the VREF input to make sure you are seeing correct voltage?

    3. Try and add some delay in "ti,vref-delay-usecs" to give the reference voltage some time to settle. 



  • Hi Aaron,

    I worry about the hardware have problem.

    Do you need some waveform of pin?

    If yes, you can tell me and I can test the pin waveform to you!