Device resetting without USB Master....1M resistor needed?

[watz]

Hi,

I have almost finished my device based on avrusb. I'm very pleased with its performance.

The device is actually an atmega8 interfacing a VFD display that is controllable by a PC via USB. When the pc is shut down, the device should be able to continue to run on its own and simply display a clock.

The little problem I have left is the fact that once the pc is shut down, the device is constantly resetting itself. I noticed that shortly after the PC is shut down, the D- line constantly switches between 0V and 3.5V resetting the atmega8 each time. Even when using an external power source for the device, the behaviour stays the same. Since the clock is set by the PC and stored in the atmega8 sram, I must not even get one single reset.

To me, it looks like the "spurious interrupt" problem described in the header. Could this actually be, and if so, would the 1M Resistor help solving the problem ?

Thx,
Watz

[watz]

...doohhh...it works now

The problem wasn't the missing 1M resistor and the watchdog but the parallel port ISP that was still attached.
Once the computer was turned off it was randomly resetting the avr

Without the isp, everything works like expected. As soon as I shut down the PC it runs and displays time + date. Once the pc is on again, PC software can access the display again.