Electronic – the common pin configuration upon microcontroller reset

gpiomicrocontrollerreset

I have looked through two datasheets and user manuals now for two different microcontrollers (LPC2387 and STM32F4xx), and I haven't found (probably missed) anywhere where the initial state of the GPIO pins was described on powerup or after reset.

My question is not specific for these MCUs, but in general, is it most common for GPIO pins to be initialized as input-floating (high-z) upon reset? Is there a standard convention, or do different MCUs do different things, and one needs to read the datasheet/manual for each MCU one works with?

Best Answer

I really don't believe that information is missing the datasheets. I have never seen it NOT there, although I have never used the particular microcontrollers you mention.

In general, at least for the micros I have used, I/O lines wake up to be as benign to the external circuit as possible. This means going to high impedance to the extent possible. In addition, pins that can be analog inputs are usually configured that way on power up. That is because digital inputs often are not intended to be held at intermediate voltages for extended time. Some might consume more power in that case, or oscillate, or do other annoying and possibly out of spec things.

However, the definative answer is in the datasheet of whatever micro you are using.

Related Solutions

Electronic – How to configure an ARM GPIO port (STR9) to an alternate function

The STR91x family of microcontrollers has very flexible peripherals. Unfortunately, this flexibility makes them somewhat complicated to set up. My suggestion is to start by downloading the STR91xFA Firmware Library from ST.com. Once you have the library linked into your project, you need to do something similar to the following:

void InitGPIO7( void )
{
   GPIO_InitTypeDef GPIO_InitStructure;

   /* Enable the GPIO7 clock */
   SCU_APBPeriphClockConfig(__GPIO7, ENABLE);

   /* Initialize the GPIO port */
   GPIO_DeInit(GPIO7);

   /* Configure pin GPIO7.3 */
   GPIO_InitStructure.GPIO_Direction = GPIO_PinOutput;
   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
   GPIO_InitStructure.GPIO_Type = GPIO_Type_PushPull;
   GPIO_InitStructure.GPIO_IPConnected = GPIO_IPConnected_Disable;
   GPIO_InitStructure.GPIO_Alternate = GPIO_OutputAlt1;
   GPIO_Init (GPIO7, &GPIO_InitStructure);
}

Note that this is untested but it should be pretty close.

Electronic – Connecting the RESET pin of AT8051

A fast search on Google gave me this:

enter image description here

The first circuit pulls the RESET pin low to enable the chip. The second circuit is the same, but with a reset button. If you press that, the chip will get reset.

Best Answer

Related Solutions

Electronic – How to configure an ARM GPIO port (STR9) to an alternate function

Electronic – Connecting the RESET pin of AT8051

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