Universal Serial Bus (USB) is a widely used interface for communication between computers and peripheral devices. In the context of microchip environments, USB connectivity can be crucial for applications such as data logging, firmware updates, and communication with sensors or other microcontrollers. This article will guide you through the process of interfacing USB with Microchip microcontrollers, specifically focusing on the PIC18F4550, which has built-in USB support.

Examples:

1. Setting Up the Hardware:

   • Ensure you have a PIC18F4550 microcontroller.
   • Connect the USB D+ and D- lines to the appropriate pins on the microcontroller (usually RC4 and RC5).
   • Use a 3.3V regulator to power the USB lines.
   • Connect the VBUS line to the microcontroller to detect USB connection.

2. Configuring the Microcontroller:

   • Use MPLAB X IDE and XC8 compiler for coding.
   • Include the necessary header files and USB library:

     #include <xc.h>
     #include <usb.h>
     #include <usb_device_hid.h>

   • Configure the configuration bits for the microcontroller:

     #pragma config FOSC = HSPLL_HS
     #pragma config PLLDIV = 5
     #pragma config CPUDIV = OSC1_PLL2
     #pragma config USBDIV = 2
     #pragma config FCMEN = OFF
     #pragma config IESO = OFF
     #pragma config PWRT = ON
     #pragma config BOR = ON
     #pragma config BORV = 3
     #pragma config VREGEN = ON
     #pragma config WDT = OFF
     #pragma config MCLRE = ON
     #pragma config LPT1OSC = OFF
     #pragma config PBADEN = OFF
     #pragma config CCP2MX = ON
     #pragma config STVREN = ON
     #pragma config LVP = OFF
     #pragma config XINST = OFF

3. Initializing the USB Module:

   • Initialize the USB module in your main function:

     void main(void) {
      USBDeviceInit(); // Initialize USB
      USBDeviceAttach(); // Attach USB
      while(1) {
          USBDeviceTasks(); // Handle USB tasks
          // Your application code here
      }
     }

4. Creating a Simple HID Device:

   • Define the HID report descriptor:

     const struct { uint8_t report[HID_RPT01_SIZE]; } hid_rpt01 = {
      {
          0x06, 0x00, 0xFF, // Usage Page (Vendor Defined Page 1)
          0x09, 0x01, // Usage (Vendor Usage 1)
          0xA1, 0x01, // Collection (Application)
          0x19, 0x01, // Usage Minimum (1)
          0x29, 0x40, // Usage Maximum (64)
          0x15, 0x00, // Logical Minimum (0)
          0x26, 0xFF, 0x00, // Logical Maximum (255)
          0x75, 0x08, // Report Size (8)
          0x95, 0x40, // Report Count (64)
          0x81, 0x02, // Input (Data,Var,Abs)
          0x19, 0x01, // Usage Minimum (1)
          0x29, 0x40, // Usage Maximum (64)
          0x91, 0x02, // Output (Data,Var,Abs)
          0xC0 // End Collection
      }
     };

   • Implement the HID report handling:

     void ProcessIO(void) {
      if((USBDeviceState < CONFIGURED_STATE)||(USBSuspendControl==1)) return;
      if(HIDRxHandleBusy(USBOutHandle) == false) {
          // Process received data
          USBOutHandle = HIDRxPacket(HID_EP, (uint8_t*)&ReceivedDataBuffer, 64);
      }
      if(HIDTxHandleBusy(USBInHandle) == false) {
          // Prepare data to send
          USBInHandle = HIDTxPacket(HID_EP, (uint8_t*)&ToSendDataBuffer, 64);
      }
     }