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TCA9539-Q1: GPIO processing speed of the TCA9539-Q1 I²C expander IC

DONGYEONG KIM
Prodigy 30 points

Part Number: TCA9539-Q1

Hello, I would like to inquire about the GPIO processing speed of the TCA9539-Q1 I²C expander IC.

In this application, the GPIOs will be configured as inputs, and we plan to use 15 pins (excluding one pin) on the TCA9539-Q1.

Each signal is expected to arrive approximately every 10–20 ms and does not have a periodic cycle like PWM.

Under this structure, even if all GPIO signals change simultaneously, we would like to ask whether the TCA9539-Q1 can process all inputs and output them via I²C without issue, and request your opinion on the approximate processing time.

Thank you.

  • 0
    TI__Mastermind 41020 points

    Hello Dongyeong,

    Our applications engineer supporting this part is current out of office. We will provide a response by early next week. Thank you!

    Regards,

    Josh

  • 0
    TI__Guru 63138 points

    Hi Dongyeong, 

    I think I already responded to a field engineer on this question. Please see my copied response below: 

    There are going to be several delays to consider.

    Once the GPIO input receives a change in state, this will trigger an interrupt on the /INT pin. This will take a max of 4 microseconds. 

    Then once the interrupt has triggered, the MCU must respond by reading an i2c transaction of the input port register that triggered the interrupt. Since there are two ports and only 1 interrupt pin, you will need to read both ports. A read transaction takes 4 bytes of data, 5 bytes if reading both input port register 0 and 1. If you read from the I/O expander at maximum speed, you can estimate about 

    5 bytes x 9 clock cycles / byte = 45 clock cycles. 

    1/400kHz  = 2.5 us

    2.5 us x 45 = 112.5 us

    4 us delay + 112.5 us = 116.5 us

    116.5 us is the combined time required to read both input port registers purely from a clock counting perspective. I am not including the timing resulting from a start condition or repeated start, or the time delay between an ACK/NACK and repeated start. So in a safe estimation, I would say you can read all 16 GPIO's within 200 us.

    Regards,

    Tyler