GPIO state at boot

Hi,

I had a question regarding the GPIO status while powering on microZed, or any Zynq devices. It is state in the datasheet that MIO pins are tristate when applied power. But based on my logic analyzer, they are individually pulled up. I had also disabled the "pull up" during PS MIO configuration in Vivado.

https://dl.dropboxusercontent.com/u/83845564/GPIO.png

I'm planning to use some of the GPIO pins for the DC-DC power enable pin in an image sensor. Thus it is imperative all these MIO pins remain low until my program turns it on otherwise.

Could someone shed light on this? Or I have to use the IO on the logic side?

Thanks in advance!

0 Former Member over 9 years ago

Connecting a logic analyzer probe to a tristated signal, with no pull up or pull down, is not going to provide a valid result. By definition the signal is neither high nor low state.

You will need to provide a pull down, either by external resistor or by enabling the internal pull down in the PS MIO configuration, to get the behavior you are looking for.

-Gary
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0 Former Member over 9 years ago

Thanks!

I didn't realized the Saleae Logic default HiZ to 1 instead of 0. The voltage measurement on a pin is 0V and pulling down with 10k resistor shows expected behavior on the SPI controller.

In the end, the logic inject 2.5V to the HiZ end. I guess this was to intended to avoid some unexpected behavior you just mentioned.
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