I was looking into the datasheet of DS4520E+ which is a 9-bit I/O expander I2C with nonvolatile memory.

In this device the default state of the I/O pins can be programmed in nonvolatile memory inside the device and upon every power cycle all the I/O pins will be set to their default programmed state from internal nonvolatile memory and this does not require or wait for establishing connection to MCU.

"Powerup default states can be programmed for the I/Os in EEPROM (with SEE = 0) and then once powered-up, SEE can be written to a 1 so the I/Os can be updated periodically in SRAM."

I have two questions.

1- What is the timing diagram of I/O pins from power down to power up. What will be the I/O state during the power cycle 'transition' ?
2- What is the default sate of these I/O pins from factory before we program the EEPROM ?

 

On system power-up, the outputs of these devices become active as soon as their supply voltage is above 2V.

They are open collector outputs, so the only sensible default is all off as a factory default. I wouldn't depend on this on anything critical.