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Original question:

Tca8418 i2c communication

TCA8418: Writing to KEY_EVENT_A register to simulate keypresses

Jason Spot
Prodigy 10 points

Part Number: TCA8418

Hello,  I am attempting to write values into register 0x04 KEY_EVENT_A register to simulate physical keypresses for lab automation validation.  Per the datasheet I should be able to read/write to any register.  However, when I attempt to write to registers 0x02 through 0x04 nothing is stored in these registers, only zeros.  

Is there a method or process to write these registers?  Is there another method which could be used to trigger the Interrupt and send the desired values to the controller from this IC?

thank you.

  • 0
    TI__Guru* 78881 points

    Hey Jason,

    The event registers are meant to be a read only register, you shouldn't be able to write data to it and have the data actually be held in that register. 

    If you wanted to simulate a key press, you could hold a col pin (assumed to be in KP mode) and row pin (assumed to be in KP mode)  low by connecting them to GND with a blue wire. 

    -Bobby

  • 0
    Prodigy 10 points

    Is the datasheet incorrect in saying "ALL REGISTERS CAN BE READ AND WRITTEN TO BY THE SYSTEM MASTER" ?   Or do I need to change the configuration to allow these writes? 

    The physical connection for the row/col would be impractical.  I'm looking to press any of the 32 keys remotely on over 100 installations.  I have access to the I2C bus remotely.

  • +1 in reply to Jason Spot
    Guru 321490 points

    That sentence means that the I²C master can do successful writes, i.e., that the TCA8418 will acknowledge all writes. It does not imply that the internal state of the TCA8418 will be affected.

    There is no method to simulate key presses only through I²C. You have to inject the events before the software that accesses the I²C bus.

  • 0 in reply to Jason Spot
    Prodigy 10 points

    Thank you Bobby and Clemens for your input, I appreciate it.