STM32H7 GPIO Default Behavior

[slc2015]

Hi,

I notice in the STM32H747XIH6 reference manual (RM0399) that 

"During and just after reset, the alternate functions are not active and most of the I/O ports
are configured in analog mode." 

I want to confirm that in "analog mode" the IO is an HZ input without internal pullup or pull-down resistor enabled? Also, can anyone confirm which I/O ports do not assume this behavior on startup (since the RM says most)? 

Thanks!

[waclawek.jan]

The reset value of GPIO registers - see the GPIO chapter in RM - reveals, which pins are not set as default (and also that most pins are in Analog mode with no pullup/pulldown).

JW

[Andrew Neil]

---

@slc2015 wrote:

which I/O ports do not assume this behavior on startup (since the RM says most)? 

---

Typically, the debug pins are an example.

[RomainR.]

Hello @slc2015 

I confirm that during and just after  RESET, except for GPIOA and GPIOB, all the others GPIO ports are in an analog mode configuration in GPIOx_MODER with the relevant bits MODERx = 0b11.

When the I/O port is programmed in an analog configuration:
• The output buffer is disabled
• The Schmitt trigger input is deactivated, providing zero consumption for every analog
value of the I/O pin.The output of the Schmitt trigger is forced to a constant value (0).
• The pull-up and pull-down resistors are disabled by hardware and Read access to the input data register gets the value 0

In RM0399 Rev 4, you can refer to section 12.3.13 Analog configuration, especially the Figure 81.

Best regards

Romain,