Second, it thickens up the contacts a bit so that they mate more tightly with the USB socket. Although I used 6 offset paths instead of the normal 4, there are still copper traces around the edge of the board. Jump to the bootloader section while the board is running, from program code. From various datasheets and other examples, I have found several things to be aware of when designing these circuits:. The finished board is below: Because I was using some non-standard parts here, I found the Ladyada and Sparkfun Eagle libraries to be useful.
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It was quite a lot of work to create a USB device from scratch, but very satisfying to figure out all the quirks xpoain make it work.
Weeks AVR USB Devices and Programming
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. For the board to ave as a USB device, it must use the USB protocol to be detected by and communicate with the computer.
This Makefile uses the LUFA build system, which requires some variables to be set properly but otherwise handles both svr building and uploading. This dplain out to be incorrect, and in fact the DFU bootloader would not be able to communicate over USB to the computer if this was the case. Note that when the device is first plugged in, it quickly flashes from red to yellow to green before displaying the lock key states.
The MCU variable is used in avr-gcc for compilation, and must be set to the right microcontroller model. Install this driver via the Device Manager:.
Makefile This Makefile uses the LUFA build system, which requires some variables to be set properly but otherwise handles both the building and uploading. To program the board again, we do have to manually reset it into DFU mode, as mentioned earlier.
You can find a useful albeit somewhat outdated guide for this here. I tested the board out in usv USB socket and read the pin voltages, just to make sure the connector will work:. The button driver requires three functions: The LED code is shown below. If there is an error, it will be purple.
This means that the binary operations are flipped: If all is working, programming is pretty straightforward:. What if we want to program the board again after this? Compared with the pins on the tiny44 and tiny45, they are much closer together and smaller.
However, this requires the fuse to be un-programmed afterward. I tested the board out in a USB socket and read the pin voltages, just to make sure the connector will work: Board drivers allow different LUFA modules to be compiled to microcontrollers on different boards while abstracting away their implementation.
Luckily, all AVR chips with hardware USB have fuses programmed by default to use the external crystal oscillator as a clock, which will work immediately as long as the crystal has a 8 MHz or 16 MHz frequency with correctly paired capacitors.
Well, when the blinking program is running, the board is not communicating over USB at all, so the system sees no device and therefore cannot program the board. Note that the schematic called for 22pF capacitors between the crystal terminals and ground, and 22 Ohm resistors on the signaling pins. After the first program, the flash needs to be erased before being programmed again, so the erase-dfu target accomplishes that.
Finally, the two most interesting parts. If a bigger program is needed, it would be time to switch to an ISP.
For the avvr, this is simply which keys are being pressed. The HWBE fuse is programmed by default to make this mode of resetting the board easy. Now, the board can be programmed. My original design had many more LEDs and switches, but it turned out I had bit off much more than I could chew – or lay out on a single-sided board.
Program the boot reset fuse, which always starts the board at the bootloader instead of the user code. Success 0x bytes written into 0x bytes memory 2. This is an epically long post about creating a USB device from scratch and programming it.