This example shows an implementation of the USB Stack Library inside of MPLAB® Code Configurator (MCC) to implement a simple USB Keypad. The AVR64DU32 family of microcontrollers (MCUs) contain a configurable Full Speed (FS) USB 2.0 transceiver.
- USB Human Interface Device (HID) Specification
- Device Class Definition for HID 1.11
- USB 2.0 Specification
- MPLAB X IDE 6.20.0 or newer
- MPLAB XC8 2.46.0 or newer
- MPLAB Code Configurator (MCC)
- AVR-Dx_DFP v2.4.286
- AVR64DU32 Curiosity Nano (EV59F82A)
- Curiosity Nano Base for Click™ Boards (AC164162)
- 2x2 Click (MIKROE-2152)
- External Button (optional)
- If not attached, the program will continue to function.
With the power off, plug in the 2x2 Click into Slot 1. Place the AVR64DU32 Curiosity Nano into the slot with the programmer USB on the left edge, as shown in the image below.
If the optional button is attached, the button is connected between AN2 (PD4) and GND. This button can be a latching push button (as shown below), or a standard push button.
Note: if using a Normally Closed (NC) button, define EXTERNAL_BUTTON_NC macro in main.c. If the button is not used, this macro should not be defined.
- Baud Rate: 9600
- Char Length: 8 bits
- Parity: None
- Stop Bits: 1 bit
| Pin | Function |
|---|---|
| PA7 | Button 3 |
| PC3 | VBUS Detect |
| PD2 | Button 4 |
| PD4 | External Button (Optional) |
| PD5 | Button 1 |
| PD6 | UART TX |
| PD7 | UART RX (Reserved) |
| PF2 | LED0 (on Curiosity Nano) |
| PF4 | Button 2 |
| PF5 | Interrupt (Reserved) |
| PF6 | SW0 (on Curiosity Nano) |
Note: Reserved pins are physically in use, but not used in the application.
Class: Human Interface Device (HID)
Protocol: Keyboard
Endpoints: CONTROL and IN
On Power-on-Reset (POR), the system initializes the peripherals and sets the application state to APPLICATION_USB_NOT_INIT. The program polls the Analog Comparator (AC) and monitors the voltage on VBUS through a voltage divider on the Curiosity Nano. When VBUS is detected, the USB initialization sequence is triggered.
Once VBUS is detected, the Nano can start the USB transceiver by calling the function USB_Start. If successful, the application transitions into the APPLICATION_USB_INIT state. If this fails USB_INIT_RETRIES times, the application moves to the APPLICATION_USB_ERROR state until the cable is unplugged.
In the APPLICATION_USB_INIT state, events from the USB host are handled by calling the function USBDevice_Handle. If data is to be sent from the MCU to the Host, the function USB_HIDKeyboardReportInSend queues a data report.
Independent of the USB state, a simple keypress state machine is called every 5 ms to handle key presses in this application. The 5 ms delay debounces the SW0 input. If the VUSB is not detected, the state machine is set to the NOT_PRESSED state, and no other actions are taken. However, if VUSB is detected, then the following occurs:
-
On POR, the state machine starts in the
NOT_PRESSEDstate. Every 5 ms, the buttons are polled to see if they are pressed. If a button is pressed, key down event(s) are loaded into a report and queued for send. The key press state machine advances to thePRESSEDstate. -
In the
PRESSEDstate, the application clears the key down events and queues the now empty report for send. This is required, as the computer will assume the button is pressed until told otherwise. The state machine advances to theHELD_WAITstate after queueing the data. -
The application waits in the
HELD_WAITstate until all of the keys are released. Once the keys are all released, the state machine returns to theNOT_PRESSEDstate.
The buttons of the 2x2 Click perform the following actions:
| Button | Keys | Function |
|---|---|---|
| 1 | CTRL + C | Copy |
| 2 | CTRL + V | Paste |
| 3 | CTRL + Z | Undo |
| 4 | CTRL + X | Cut |
| SW0 | "AVR DU" | Prints the string "AVR DU" |
| External Button (Optional) | ALT + F4 | Closes the running program |
Note 1: SW0 is located on the Curiosity Nano.
Note 2: Set the macro EXTERNAL_BUTTON_NC for buttons that are normally closed.
Note 3: The 2x2 Click debouncing causes the buttons to be held for an extra ~0.5s. The code is designed with a one-shot to prevent this from causing issues, however quickly switching buttons or tapping is not possible.
This example has shown how to implement the USB Stack Libray on the AVR64DU32 family of MCUs as a USB Keypad.