4.4 PORT Example

This subsection contains an example on how to configure a PORT to turn on an LED when pressing a user button. To identify which pins of the microcontroller are routed to the user LED and to the user button, the used board schematic is necessary. For the AVR128DA48 Curiosity Nano board used for this example, the LED is connected to the sixth pin of PORTC, PC6, and the button is connected to the seventh pin of PORTC, PC7. To make sure this is the correct configuration of the pins, the user must check the board schematic.

The code below shows how to write code for turning on and off an LED, using bit position macros.

/* Direction configuration of the pins */ 
/* Read-Modify-Write: Software */
PORTC.DIR |= (1 << PIN6_bp);               /* Output for the user LED */
PORTC.DIR &= ~(1 << PIN7_bp);              /* Input for the user button */
PORTC.PIN7CTRL |= (1 << PORT_PULLUPEN_bp); /* The pull-up configuration */
while (1)
{
    if(PORTC.IN & (1 << PIN7_bp))          /* Check the button state */
    {
        /* The button is released */
        PORTC.OUT |= (1 << PIN6_bp);       /* Turn off the LED */
    }
    else
    {
        /* The button is pressed */
        PORTC.OUT &= ~(1 << PIN6_bp);      /* Turn on the LED */
    }
}

The code below provides the same functionality but using the bit masks.

/* Direction configuration of the pins */
/* Read-Modify-Write: Software */
PORTC.DIR |= PIN6_bm;               /* Output for the user LED */
PORTC.DIR &= ~ PIN7_bm;             /* Input for the user button */
PORTC.PIN7CTRL |= PORT_PULLUPEN_bm; /* The pull-up configuration */
while (1)
{
    if(PORTC.IN & PIN7_bm)          /* Check the button state */
    {
        * The button is released */
        PORTC.OUT |= PIN6_bm;       /* Turn off the LED */
    }
    else
    {
        /* The button is pressed */
        PORTC.OUT &= ~(PIN6_bm);    /* Turn on the LED */
    }
}

Also, the SET and CLR registers can be used to set and clear the pin value without Read-Modify-Write operations, as shown in the code below. This allows performing the setting and the clearing of the desired value using an atomic instruction, instead of reading the register value first. The main advantage is that this action cannot be interrupted. Only one instruction is executed instead of three (Read-Modify-Write).

PORTC.DIRSET = PIN6_bm;             /* Output for the user LED */
PORTC.DIRCLR = PIN7_bm;             /* Input for the user button */
PORTC.PIN7CTRL |= PORT_PULLUPEN_bm; /* The pull-up configuration */
    
while (1)
{
    /* Read-Modify-Write: Hardware */
    if(PORTC.IN & PIN7_bm)          /* Check the button state */
    {
        /* The button is released */
        PORTC.OUTSET = PIN6_bm;     /* Turn off the LED */
    }
    else
    {
        /* The button is pressed */
        PORTC.OUTCLR = PIN6_bm;     /* Turn on the LED */
    }
}

Another way to configure the direction and set/clear the value of the output pin is by using virtual ports, as presented in the code below.

/* Direction configuration of the pins */
/* Read-Modify-Write: VPORT registers */
VPORTC.DIR |= PIN6_bm;              /* Output for the user LED */
VPORTC.DIR &= ~PIN7_bm;             /* Input for the user button */
PORTC.PIN7CTRL |= PORT_PULLUPEN_bm; /* The pull-up configuration */
while (1)
{
    if(VPORTC.IN & PIN7_bm)         /* Check the button state */
    {
        /* The button is released */
        VPORTC.OUT |= PIN6_bm;      /* Turn off the LED */
    }
    else
    {
        /* The button is pressed */
        VPORTC.OUT &= ~PIN6_bm;     /* Turn on the LED */
    }
}