Compared with the pins on the tiny44 and tiny45, they are much closer together and smaller. One important note is that the entire chip has to be erased before you can run other commands on it. Basically, this is a keyboard with just three keys. The USB signaling pins require resistors for impedance matching to optimize signal quality. After the first program, the flash needs to be erased before being programmed again, so the erase-dfu target accomplishes that.

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For the keyboard, this is simply which keys are being pressed.

To run the uploaded program, one can just do dfu-programmer target reset or pull out the board and plug it back in. In the class inventory, we have a couple of devices with hardware USB support: Program the boot reset fuse, which always starts the board at the bootloader instead of dplain user code.

My buttons are connected to pins 1, 4, and 7 on port D, so the implementation is straightforward. Note that this makes the pads narrower than the pins, so soldering will be harder.

The rightmost button on the board connects PD7 and GNDso it can be pressed during reset to trigger this condition. This has been a long post.

AVR Xplain

This Makefile uses the LUFA build system, which requires some variables to be set properly arv otherwise handles both the building and uploading. If there is an error, it will be purple.


The LED code is shown below. Board Drivers Board drivers allow different LUFA modules to be compiled to microcontrollers on different boards while abstracting away their implementation. The Eagle libraries also include supply parts which make it easier to create VCC and GND connections by dropping parts instead of naming nets. Adapting from wvr demo, the code for this is pretty straightforward: The project files are arranged as follows. What if we want to program the board again after this?

A completely custom LUFA application would use the low-level modules to interact directly with hardware, and a custom driver on the host to acr with the device. On the other hand, microcontrollers with hardware USB support offload the necessary computations to dedicated circuitry. If all is working, programming is pretty straightforward: This is the board, usn laid out.

If a bigger program is needed, it would be time to switch to an ISP. After many hours of routing, I came up with this compact, symmetric design using the integrated USB connector. Adapting from the demo, the code for this is pretty straightforward:. I shaved these unwanted copper parts off with an X-acto knife. For the board to appear as a USB device, it must use the USB protocol to be detected by and communicate with the computer.


Weeks AVR USB Devices and Programming

To program the board again, we do have to manually reset it into DFU mode, as mentioned earlier. If this capacitance is far off, the crystal can xlpain slower or faster than intended. This just temporarily enters the bootloader.

The code below will defines the LED color to be red, yellow, and green as the device is powered on, enumerating, and ready, and purple if there is an error. Note that I could not have implemented things as below if xplaim LEDs were on the same pin number of different ports, due to the way the mask is used to select LED pins. First up is to define masks in Keyboard. Success 0x bytes written into 0x bytes memory Jump to the bootloader section while the board is running, from program code.

This serves two purposes. That was a lot of stuff, but if all goes well, we should have a limited functionality keyboard which is able to type three letters, and display the system lock key states!

The board then shows up as ATmega16U2 under libusb-win32 devices when the bootloader is running.