No announcement yet.

Using Can-Interface of the Beaglebone Black while using a Touch-Display

  • Filter
  • Time
  • Show
Clear All
new posts

  • Using Can-Interface of the Beaglebone Black while using a Touch-Display

    I am trying to use one of the two CAN-Interfaces with the Beaglebone Black (can be muxed on P9.19; P9.20 or P9.24; P9.26), while also using a resistive Touchdisplay (Gen4-4dcape-70T). Unfortunately the Display uses both Can-Pins in a diffrent pin-muxing.

    P9.26 is used as an interrupt pin for the Touch Controller of the display. So this ones out.

    P9.19/P9.20 are used as i2c pins. I have figured out, that if I remux these Pins in runtime (When the display is already initialized and working) and use the Can-Interface instead (The display still works then). But if I let the Can-cables coming from a Can Transceiver in the Pin-Slots (P9.19/20), when starting the Beaglebone, the display won't start. I see several approaches here and would like to know what you would prefer. I have to create a Custom-cape, so rerouting is no problem.
    1. Use a signal-Multiplexer which is controlled by a GPIO-Pin.
    2. Put the Interrupt on a diffrent pin
    Why does the Display use both i2c pins? And why is i2c2 only needed for the initialization?

    Thank you!

  • #2

    Sorry for the delay.

    The display uses I2C as per its schematic (refer to both the gen4-4DCAPE-70T schematic as well as its Adaptor, in the same datasheet). One of the I2C (I2C2) is for the EEPROM as per the CAPE standard, which tells the BBB what cape is connected on the Bus, this is the P9.19 and P9.20 I believe you are referring to. I am unsure if these pins are designed to be used by user code etc as you are trying to, as I was under the impression they are dedicated for the CAPE manager and identifying connected CAPEs, but I may be mistaken.
    The other (I2C1) which is P9.17 and P9.18) is used for the touch controller and can be used with other User I2C devices also, provided they don't have conflicting addresses - as as any usual I2C bus system.

    We do not control the software for the display CAPE's, they are controlled and updated accordingly by the engineers at, our hardware is just compatible with what was existing, other than the addition of our touchscreen drivers which they include in the releases.

    Sorry I dont have any answers to satisfy your questions really, I am not sure what is best and how you can best utilise CAN on the Beaglebone black. You might need to approach the forums and get support there.

    On the Adaptor schematic, there are some Red designators which just go to the optional 'Button-FPC' which are not used in software at all unless the Users add it, so these pins are not utilised.

    You could attempt to move the Touch_IRQ from P9.26 to somewhere else, you likely will have to adjust something in the software to make this happen though - which sadly I am not able to assist with. If you can achieve that, then you could use those pins for your CAN I would imagine. This would be the only viable option I think, given the I2C which is for the CAPE identification.

    Sorry I cant be of much more help