Objective Development Forums

3 V is enough to be recognized as high level. When the AVR outputs +5V on D+ or D-, the diodes limit the voltage to 3.6 V, which is also accepted as high level inside the common mode range of the input amplifier, although it's slightly outside the spec. 3.6 V is a compromise between a too low level ...

If you have set all CKSEL bits to 1, you have programmed the ATMega8 for external clock. Just apply any clock (e.g. generated with a 555) to the XTAL1 pin (pin 9 on the DIL package). Make sure that the clock is several times the ISP clock. 500 kHz to 1 MHz should be OK.

I know only one programmer which implements Parallel Programming and that is the STK500. There's also a reverse engineered circuit for an STK500 available on the net, if you don't want to buy one. What may be easier to obtain is a "parallel enabler" or whatever the name of that circuit is....

If the device is really recognized by Windows, then USB communication must be working. If Windows knows the device name, it was able to read the device descriptor. If it just claims to have an "unknown device", it does not recognize it. Trapezoid waveforms are OK on the scope, but real tri...

The signedness-warnings are harmless. The assembler warnings are probably a bug in gcc since it seems to produce code which is not well understood by the assembler. I don't know whether these warnings are relevant.

This is a bit tricky. If you send 8 bytes with usbSetInterrupt(), the host asks for the next chunk until it receives less than 8 bytes and merges all chunks to a common message. This means that you should send the first 8 bytes with usbSetInterrupt(), then wait until they have been sent to the host ...

I don't know what this recent change does to break CDC ACM devices on low speed USB, but I can tell you that interrupt- and bulk-endpoints are equivalent except that bulk endpoints are polled "as fast as possible" while interrupt endpoints are polled with a given rate.

See the Makefile, target "fuse". If you type "make fuse", it flashes the fuses.

Are you sure that these questions are related to AVR-USB (a firmware implementation of USB on AVR microcontrollers) or to a project based on AVR-USB?

Any real time protocol with tight time constraints gets into troubles with USB -> serial converters since the timing can usually not be exactly preserved. USB CDC sends data on the stream endpoint when it is available. If no data is available, no data is sent. If the time resolution after going thro...

This is not correct. The vector table is in flash memory.

The vector table consists of relative jump instructions. You must compute the correct rjmp instruction and write it to the vector table slot. Please note that flash memory can only be programmed page-wise. You must read the entire page, modify the vector and write back the page. Also, some AVRs requ...

Since the interrupt vector is in flash memory, it's hard to modify it from your code. I would recommend that you define ISRs for INT0 AND INT1 and call your routine from either one.

You must return -1 (0xff) in usbFunctionSetup() to inform the driver that you want to receive the data via usbFunctionWrite(). See the documentation in usbdrv.h.

You need to know how the HID report descriptor should look like for a composite device. You have two options to find this out: (1) You read the USB HID spec and design your descriptor from scratch, or (2) you look at the HID report descriptor of an existing device and modify it according to your nee...