Hi team,
There are 2 questions about TCA9539-Q1:
- Whether a reset is needed after VCC is on
- Before manipulating IIC read and write, do I have to pull up reset , and then pull down reset again?
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Hi team,
There are 2 questions about TCA9539-Q1:
There is an automatic power-on reset.
There is no need to do a reset later, unless you actually want to re-initialize all registers.
Hazel,
As Clemens said, when power is cycled, the device will automatically reset. And there's no need to reset when performing I2C read or writes.
Regards,
Eric Hackett
Hi Eric,
There may be another issue: when power on TCA3539 the status of INT is always low(my customer want to use INT to monitor changes in GPIO). After reset ,INT changes to high and the function is normal.
What should I do to analysis this?
During power up, the input buffers do not yet work correctly, so it is indeed possible that a voltage change is detected.
In any case, you should clear the interrupt after you have configured the pins.
You mean that this issue may be caused by the timing?
And how does customer validate this?
How to avoid this?
This issue is unavoidable. When powering up, there is no previous state, so it is likely that the actual state is different from what the device thinks the previous state was.
Hazel,
There are two ways you can address the asserted INT.
1) Toggle #RESET after you power up
2) read all of the input registers after power up.
This will reinitialize the state machine.
INTs triggering immediately after power is usually due to the state of the p-ports during the Vcc ramp up. I believe the 'default' input state of the p-port is clocked in at the PoR threshold. If you have a large RC constant like a large pull up on the p-port then the transition from low to high can occur after power up and trigger the INT.
-Bobby