The 'pic16f15244-ioc-example' code example uses the PIC16F15244 Curiosity Nano Development board to demonstrate how to transmit "Button pressed!" to a PC terminal application each time the Nano's push-button (SW0) is pressed. The example highlights the use of the Interrupt-on-Change (IOC) and EUSART (Enhanced/Addressable Universal Asynchronous Receiver Transceiver) modules.

• PIC16F15244 Product Page

• MPLAB® X IDE 6.10 or newer (microchip.com/mplab/mplab-x-ide)
• MPLAB® XC8 2.41 or a newer compiler (microchip.com/mplab/compilers)
• MPLAB® Code Configurator (MCC) 5.3.7 or newer (microchip.com/mplab/mplab-code-configurator)
• Microchip PIC16F1xxxx Series Device Support (1.18.352) or newer (packs.download.microchip.com/)

• PIC16F15244 Curiosity Nano
• Micro-USB to USB 2.0 cable

1. Connect the PIC16f15244 Curiosity Nano board to a PC using the Micro-USB to USB 2.0 cable.
2. If not already on your system, download and install MPLABX IDE version 6.10 (or newer).
3. If not already on your system, download and install the XC8 C-Compiler version 2.41 (or newer).
4. Open the 'pic16f15244-ioc-example.X' project as shown in Figure 1.

5. Click -> Project Properties button to open the Project Properties window. Select the Curiosity tool from the Tools drop-down menu as shown in Figure 2.

6. Press the 'Make and Program Device' button to program the PIC (see Figure 3). Verify that the device was successfully programmed (see Figure 4).

7. For Windows PC: Open a terminal program. For this example, Tera Term was used as the terminal program.

a. Select the port that is used by the Nano board as shown in Figure 5.
b. Configure the serial port as shown in Figure 6.

8. For MacOS: Open a terminal program. For this example, open a Terminal.app window. We shall use screen as the terminal program.

a. With the project loaded in MPLAB & the Curiosity Nano board connected to the Mac's USB port: Find the tty device being used:

```zsh  
% ls -l /dev | grep tty.usb          # search for a tty.usb connection  
crw-rw-rw-  1 root    wheel           18,   4 May  8 01:06 tty.usbmodem14102  
%  
```  

b. start screen in Terminal.app & configure the serial port in one command:

```zsh
% screen  /dev/tty.usbmodem14102 9600  
```  

This creates a connection to the serial port and enables messages to appear "screen" on Terminal.app when the button is pushed.
Note: The tty will change from time to time, but will always begin with `.usbmodem`

After the Nano board is programmed, the EUSART module will transmit the string "Button pressed!" to the PC terminal window each time push-button SW0 is pressed.

Input pin RC2 is connected to the output of SW0. Pin RC2 is pulled to a logic 'HIGH' state during normal operation. When SW0 is pressed, the internal circuit of the button makes a complete connection, allowing the voltage to flow through the pin to ground. When this transition of a logic 'HIGH' to logic 'LOW' occurs, IOC hardware detects this change and issues a negative-edge interrupt. The Interrupt Service Routine (ISR) will then clear the IOCCF flag and transmit the string 'Button pressed!' over the EUSART. The IOC edge selection can be configured in MCC as shown in Figure 7.

Output pin RC0 is configured as the TX output through PPS. Nano hardware also connects pin RC0 to the USB receive line, allowing a quick connection to the PC terminal without any additional wires or USB bridge circuits.

The EUSART module is configured to use the printf() function call that it built in to the XC8 libraries. In MCC, check the 'Redirect Printf to USART' check-box as shown in Figure 8, and the additional function calls are added to the project. Example 1 shows the use of the printf() function in the IOC ISR.

void SW0_ISR(void)
{
    // Add custom IOCCF2 code
    // Call the interrupt handler for the callback registered at runtime
    if(SW0_InterruptHandler)
    {
        SW0_InterruptHandler();
    }
    IOCCFbits.IOCCF2 = 0;
}

static void SW0_UserCallback(void)
{
     printf("Button pressed! \r\n");
}

The 'pic16f15244-ioc-example' code example uses the PIC16F15244 Curiosity Nano Development board to demonstrate how to transmit 'Button pressed!' to a PC terminal window each time push-button SW0 is pressed. The example uses the Interrupt-on-Change (IOC) module to detect a positive to negative-edge transition on the input pin, and the EUSART module to transmit the string 'Button pressed!' to the PC terminal window.