V-USB level converter + 1.5k pull-up on D-

[hxhl95]

Hi all,

I have an ATmega328p which has its PD2 as D+ and PD3 as D-, as per the V-USB default setup. However instead of diode clamps to enable my 5V ATmega to talk to the 3.3v USB bus lines, I have used a different level converter. A schematic of the level converter:



Question: I'm not quite sure what to do with the 1.5K pull-up resistor that is supposed to be on D-. Assuming SH in the above circuit goes to PD3 (D- pin on the ATmega), should I replace R1 with a 1.5K resistor? Should the 68 ohm series resistors go on the SH or the SL side, if they are critically necessary at all?

Due to a certain unfortunate series of events I can no longer change the hardware for the level conversion very much, so I would appreciate some input on how to get V-USB to enumerate properly using this level converter.

Thanks

[ulao]

I can't tell exactly what your setup is without seeing the entire schematic but:

" I'm not quite sure what to do with the 1.5K pull-up" -- Yes you need it, yes it goes on the d-. Releasing this drops the USB.
" Should the 68 ohm series resistors go on the SH or the SL side, if they are critically necessary at all?"-- Just make sure the are on the side that is closes to the chip.

Personally I dont think the USB will work without the diodes. If it gives you troubles run your device in to a hub first. Seems that in my experience they are not needed on some hubs ( i.e belkin ).