about imx8 POR_B signal

[heiyouheiyoubaluobo]

My project uses imx8qxp. I have a question about the POR_B signal.

the minimum duration of POR_B in the manual is 1 RTC_XTAL clock cycle, that is, 30us.  The manual is  IMX8QXPAEC   Rev. 4, 01/2022 , p51.

If the power supply voltage and crystal oscillator of imx8 are maintained in normal working state, and remain unchanged,  only pull down POR_B, must the pull down time be greater than 30us? Now in this case I pull down POR_B for 640ns and it can still reset successfully. I want to ask what is the minimum pull-down time of POR_B in this case?

[JosephAtNXP]

Hi,

Thank you for your interest in NXP Semiconductor products,

The time would still be the same, minimum 30 us.

POR is meant for the voltages to reset the processor, the PMIC does the sequence for the power-down while drives low the signal, then performing the power-up sequence and rising the POR_B causing the pins to be polled.

The device supports 16 boot modes but only several are supported on the chip and the
others are reserved for future use. BOOT_MODE is initialized by the System Controller
sampling the SCU_BOOT_MODE inputs on the rising edge of POR_B. After these
inputs are sampled, their subsequent state does not affect the contents of the
BOOT_MODE stored in the System Controller.

You could do a SW reset if the supplies don't need to be restarted.

Software reset (Host only) is initiated by the write operation on the RSTD, RSTC, or
RSTA bits of the System Control register to reset the data part, command part, or all
parts of the host controller, respectively.

Regards