Electrical – How to disable a microcontroller port once enabled

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I'm using MP430 series microcontroller. The functionality of the code is to do a specific task and then don't do anything (sense the tilt and glow an LED in a fixed amount of time). But due to some bug in the code, I'm noticing that a port pin gets '1' after some time.
So now I want to disable all the ports once the task is completed. How can I disable these ports which initially I defined as Input and Output ports.

And my 2nd question is: if I'm disabling these ports then are there any chances that the output port (now disabled) will stay floating and generate some noise or something and trigger my output LED? This question is for all the microcontrollers (MSP430, PIC, AVR, etc.)

Best Answer

Pretty much every microcontroller will have it's ports' default state as 'input'. So just set the ports as inputs and you should be all set. One potential gotcha is if the pin has an internal pull-up or pull-down set, which could cause some issues, depending on your circuit. Lastly, most datasheets provide the default state of the bits in a given register. So to get the register back to how they were after the chip powered on, simply set the bits to their default state.

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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 – Safely connecting 4056 and MSP430

One popular method to get data from one device running off one power supply to some other device running off some other power supply -- perhaps at much higher voltage -- is to solidly connect the grounds together and use a "discrete inverter" (level shifter) built from one discrete FET and one resistor for each signal (in your case, 5 signals).

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Your MSP430 drives the gate of the FET. When the MSP430 sends a "hi" output (+3.3 V), turning the FET "on", the FET pulls the output close to GND. When the MSP430 sends a "lo" output, turning the FET "off", the resistor -- with one end connected to the "other" power supply, the power supply connected to the 4056 -- pulls the output "hi". In your case, the output is pulled close to +12 V when your +12 V power supply is turned on and connected, or 0 V if it isn't. No constant current can leak through this inverter / level shifter.

This arrangement "inverts" the signal. In principle one could add another inverter (a single 74HC14 or 5 more transistors and resistors) in series so that "hi" input gives "hi" output, and "close to GND" input gives "close to GND" output, but many people make the hardware a little simpler at the cost of adding a few more lines of code to compensate.

As an alternative to the one FET one resistor discrete inverter, some people use a "discrete inverter" built from one discrete BJT and two or three resistors for each signal; it works very similarly. a b c

Best Answer

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

Electronic – Safely connecting 4056 and MSP430

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