How to use UPDI Pin as GPIO Output on ATtiny804 ?

[krishank652]

Dear All,

I need help configuring a GPIO pin as an output on my ATtiny804. I require an additional output pin for my circuit, and I would like to use the UPDI pin11 (physical pin 10).

Here’s an example code I tried (not working):

// Pin 11 is used as the output pin
const int outputPin = 11;

void setup() {
  // Initialize pin 11 as an output
  pinMode(outputPin, OUTPUT);
}

void loop() {
  // Turn the LED on
  digitalWrite(outputPin, HIGH);
  delay(100); // Wait for 100ms

  // Turn the LED off
  digitalWrite(outputPin, LOW);
  delay(2000); // Wait for 2 seconds
}

Could someone guide me on how to properly configure the UPDI pin as a GPIO output? Any suggestions or example code would be greatly appreciated!

Thank you in advance!

[jvasileff]

If you configure the UPDI pin for GPIO, you'll no longer be able to re-program the chip without a high voltage programmer, so make sure the extra GPIO is worth the effort.

There are notes on how to enable GPIO at https://github.com/SpenceKonde/megaTinyCore?tab=readme-ov-file#list-of-tools-sub-menus - search for the text "Tools -> UPDI/Reset".

An alternative is to use the UPDI pin as an input, with some limitations. I haven't tried it myself, but see #380

[krishank652]

Thanks for a suggestion,

I can use Input. Can you please tell me the limitation?

I have a push button in circuit, i can use it for this signal.. Can you please tell me how to use?

[jvasileff]

See Spence's comment in the link I posted.

You'll want to avoid using external pullup or pulldown resistors, which would interfere with programming. Also don't press the button when programming.

[krishank652]

I initially used an input pin without an external pull-up resistor, but the input readings were fluctuating. Now, after adding an external pull-up resistor, it works fine.

While programming, I removed the resistor, and after uploading the code, I connected a 10k resistor between GND and the UPDI pin.

Can you please review my circuit to check if it’s correct? Also, is this the proper way to use an input pin on the UPDI?

Test Code:

// Pin definitions
const int buttonPin = 11; // Push button connected to pin 11
const int ledPin = 9;    // LED connected to pin 9

// Variables to store button state
bool buttonState = false; // Current state of the button
bool lastButtonState = false; // Previous state of the button
bool ledState = false; // Current state of the LED

void setup() {
  pinMode(buttonPin, INPUT_PULLUP); // Configure button pin as input with internal pull-up resistor
  pinMode(ledPin, OUTPUT);          // Configure LED pin as output
  digitalWrite(ledPin, LOW);        // Turn off the LED initially
}

void loop() {
  // Read the current state of the button
  buttonState = digitalRead(buttonPin);

  // Check if the button state has changed from the last state
  if (buttonState == LOW && lastButtonState == HIGH) {
    // Toggle the LED state
    ledState = !ledState;

    // Update the LED output
    digitalWrite(ledPin, ledState ? HIGH : LOW);
  }

  // Save the current button state for the next iteration
  lastButtonState = buttonState;
  
}

[hmeijdam]

Now you need to disconnect the 10K resistor if you want to program. If you put your pushbutton between GND and UPDI, you automatically use the internal weak pullup resistor from the UPDI pin instead, and you don't need to change anything when you want to program.
UPDI programming is impossible with the 10K resistor in place, which can be a disadvantage or an advantage, based on your requirements.

[krishank652]

Now you need to disconnect the 10K resistor if you want to program. If you put your pushbutton between GND and UPDI, you automatically use the internal weak pullup resistor from the UPDI pin instead, and you don't need to change anything when you want to program. UPDI programming is impossible with the 10K resistor in place, which can be a disadvantage or an advantage, based on your requirements.

thanks, working perfect. now i removed 10k registor and directly used pushbutton between gnd and updi pin

[krishank652]

Dear @hmeijdam,

I updated my circuit as below. Is this ok and correct way?

I tested it and working fine.

Code tested

// Pin definitions
const int buttonPin = 11; // Push button connected to pin 11
const int ledPin = 9;    // LED connected to pin 9

// Variables to store button state
bool buttonState = false; // Current state of the button
bool lastButtonState = false; // Previous state of the button
bool ledState = false; // Current state of the LED

void setup() {
  pinMode(buttonPin, INPUT_PULLUP); // Configure button pin as input with internal pull-up resistor
  pinMode(ledPin, OUTPUT);          // Configure LED pin as output
  digitalWrite(ledPin, LOW);        // Turn off the LED initially
}

void loop() {
  // Read the current state of the button
  buttonState = digitalRead(buttonPin);

  // Check if the button state has changed from the last state
  if (buttonState == LOW && lastButtonState == HIGH) {
    delay(50); // Add a small delay to debounce the button

    // Read the button state again to confirm it's stable
    if (digitalRead(buttonPin) == LOW) {
      // Toggle the LED state
      ledState = !ledState;

      // Update the LED output
      digitalWrite(ledPin, ledState ? HIGH : LOW);
    }
  }

  // Save the current button state for the next iteration
  lastButtonState = buttonState;
}

[hmeijdam]

That's how I would wire it if using the UPDI as input.