• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 33 subscribers
  • Views 327 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TCA6418E: Question about register operation

user4976860
Prodigy 50 points
Part Number: TCA6418E
Other Parts Discussed in Thread: TCA8418E, TCA8418

Hi TI Support Team,

I have questions about register description of TCA6418E.

In register map, there is mention such as "read twice to clear" at GPIO_DAT_STATx registers.
Is this surely about status register, not interrupt register?

In register descriptions, on the other hand, it says GPIO_INT_STATxs are cleared on read (not mentioned "twice"), but no description about GPIO_DAT_STATx clear.

Could you tell me what is the actual operation of those registers?

Thanks.

  • 0
    TI__Guru 69050 points

    Hello,

    This device is a modified (different die, features removed) of the keypad scanner: TCA8418E.

    I believe the GPIO_DAT_STAT could store 2 values inorder to detect when when the signal went low and then high (like a key press and then release). This would likely be why it recommends to reads, to make sure you got both events.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 50 points

    Thank you for your reply.

    Hmm... I believe typical I/O expander doesn't have any buffer so the host can read immediate value of I/O port but you mentioned this device is different one.

    Is it sure we have to read GPIO_DAT_STAT twice and pick second one to get latest value?
    What would occur if we read GPIO_DAT_STAT more than twice?

    Additionally I found TCA8418, you mentioned as original device, scans the GPIO with 25ms interval so the latency is too large.
    https://e2e.ti.com/support/interface/f/138/t/673472
    Is it same for TCA6418E?

  • 0 in reply to user4976860
    Prodigy 50 points

    Hello Support Team,

    I'm sorry to be bothering you but could you answer to the question?

    Thanks.