PCA9555: About whether it will reset after reading GPIO high/low.

Ariel Chang

Prodigy 20 points

Part Number: PCA9555
Other Parts Discussed in Thread: TCA9555

Dear TI members,

Due to the design of the PCA9555, we have some questions.

We are wondering if it is necessary to clear INT after reading GPIO high/low?

If necessary, Any suggestions on how to clear it?

We reference (+) PCA9555: Question on PCA5555 Interrupt Behavior - Interface forum - Interface - TI E2E support forums

Due to the described "Going forward now, I will address the question you've presented assuming the TCA9555 is selected because the INT function is easier to predict."
Does the case also apply to PCA9555?

Thanks.

Ariel

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 317370 points

This is described in section 8.4.1 of the datasheet. Reading the port register clears the interrupt status for the bits in this register.

As a 16-bit expander, it has two port registers. You might need to read both.

0 Ariel Chang over 2 years ago in reply to Clemens Ladisch

Prodigy 20 points

This means that if we want to clear the interrupt, we need to read the port register.
If correct, we can read the registers via the I2C bus.
For example, if we want to clear the interrupt on port 1, we only need to send the Input Port 1 command, right?

0 Clemens Ladisch over 2 years ago in reply to Ariel Chang

Guru 317370 points

If you know that the interrupt came from port 1, then you need to read only from port 1.

But how do you know the source of the interrupt, or the number of changed bits? You can be sure only if all bits of the other port are configured as outputs.

0 Jack Guan over 2 years ago in reply to Clemens Ladisch

TI__Mastermind 41216 points

Hey Ariel,

I agree with Clemens response here. To add on- if you are unsure where the interrupt is coming from, you can read both port registers to ensure that the interrupt gets cleared as he mentioned previously as well.

Please let us know if any further clarification is needed!

Regards,

Jack

0 Ariel Chang over 2 years ago in reply to Jack Guan

Prodigy 20 points

Hi Jack,

So if I want to clear INT, no matter whether the port has an interrupt or not, I just need to read all the ports to achieve the purpose of clearing the interrupt?

Thanks.

Ariel

0 Ariel Chang over 2 years ago in reply to Ariel Chang

Prodigy 20 points

Dears,

But our design separates the IO expander and other device registers.
In this case, how do we know the interrupt from the IO expander?

What additional steps should we implement?

Thanks.

Ariel

+1 Clemens Ladisch over 2 years ago in reply to Ariel Chang

Guru 317370 points

If the interrupt is shared with other devices, then you have to read both registers to check if they have changed.