Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 4 of 4

Thread: Multiple devices on SPI buss RA8875 Tri-Sate issue

  1. #1
    Senior Member
    Join Date
    Apr 2020
    Location
    Guelph Ontario Canada
    Posts
    116

    Multiple devices on SPI buss RA8875 Tri-Sate issue

    I know there is an issue with Tri-stating on the SPI buss with RA8875 displays ..

    the question I have is if you have 2 devices on the SPI buss that have their own CS lines ...
    Is the tri-state problem still there ?

    or is the SPI Buss corrupted due to conflict with the state of the RA8875 when the other SPI device is selected?

    Thanks .. need some schooling here

    Keith

  2. #2
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Location
    Ayer Massachussetts
    Posts
    4,035
    Paul's paper on better SPI design (https://www.pjrc.com/better-spi-bus-design-in-3-steps/) would indicate that SPI devices having their own CS lines does not prevent the need for tri-stating. The first step might be to add pull-up resistors to the CS and reset lines. But if you are still having problems, you may need to add a tri-state buffer for each display.

  3. #3
    Senior Member
    Join Date
    Dec 2016
    Location
    Montreal, Canada
    Posts
    3,700
    Tri-state is not a CS issue unless you have both CS' asserted. The issue is at MISO, some chips don't tri-state that line and it fights with the other slave that is ran in parallel. tri-state buffers exist for these problems

  4. #4
    Senior Member
    Join Date
    Apr 2020
    Location
    Guelph Ontario Canada
    Posts
    116
    Thankyou for the reply .. I'm struggling with the Ra8876 display which is 7.84" 1280 X 400 pixels and requires SPI for 2 chips on the board SSD2828 is the bridge chip from SDI to MIPI and needs to be set to allow the the passthrough for the ra8876 ... I've tried the forked version ra8876teensylite library which bit banged the other connection but its not working ...So trying to see what can be done..Thanks for the info

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •