PCA9555: The I/O port can be read as a power-on reset (input state when the power is turned on), but in actual use it seems to be in the output state when the power is turned on

Conor

Guru 12050 points

Part Number: PCA9555
Other Parts Discussed in Thread: TCA9535

Hi,

On the data sheet, the I/O port can be read as a power-on reset (input state when the power is turned on), but in actual use it seems to be in the output state when the power is turned on. (The LED to which the port is connected is lit.) Since there are discrepancies with the description in the datasheet, could you give us your opinion on possible causes?

Thanks,

Conor

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 316440 points

The I/O pins have built-in pull-up resistors.

If you do not want pull-up resistors, use the P/TCA9535.

0 Tyler Townsend over 2 years ago

TI__Mastermind 46888 points

Hi Conor,

I am assuming that the 100k internal pull-up resistor might be what you are seeing. Do you have a schematic on hand to confirm this?

If LED's anode is connected to the pin, and the cathode to ground, there might be some light emitting from the diode due to the internal pull-up present on the p-port.

Regards,

Tyler

Interface

Interface forum

PCA9555: The I/O port can be read as a power-on reset (input state when the power is turned on), but in actual use it seems to be in the output state when the power is turned on