atmega 8 new product with v-usb project?

[newhero]

Recently I'm making some of usb interfaces with atmega8 using rom files originated from V-Sub Project.
I found that on same board some chips are working good some chips no.
I tried to figure out what's the difference between those chips.
The only thing I found is chip model numbers (Even I don't what the numbers means) following "ATMEGA8-16PU" or "ATMEGA8-16AU".
Those are all still working good with other Rom Files.
Is anybody experienced this like me?

Thanks.

[Daid]

The AU/PU are different packaging types (see section 29 of the ATMega8A datasheet "ordering information")

I also have a few ATMega8 chips that are not working with V-USB. But I'm overclocking the AVR to 20Mhz. So I think my problems are related to the 20Mhz (as 16Mhz is max according to the datasheet)

V-USB seems to be quite picky about the signals. So to maximize succes, I do the following:
-Enable the brown-out detector (solved hanging on plugin problems)
-100nF cap at the AVR on power/ground.
-100uF cap on the supply.
-Made sure all my solder connections are nice and clean.
-Made the PCB traces with D+ and D- as short as possible, and as close to each other as possible (so if they catch interference, both lines are more likely to catch the same) And no 90 degree bends, as 90deg bends are more likely to emit electrical interference.
-Use a proper USB cable.

[newhero]

Thank you for your reply.
I tried with many ATmega8 16PUs and ATmega8 16AUs.
Still I'm waiting for the answer from atmel, but some of users told me that they changed some silicon base format for newly made ones. I don't know even it does afffect a lot in electrical charicteristics or not.
But even with the poor designed circuit, if I'm using the same chip with same fusebits and same firmware then those should be working good anyway.
Only working good atmega with V-usb based circuit are newly made ones.
For ATmega8 16PU, I have year '06 made one and year '11 made ones(5 ones). only year '06 working.
For ATmega8 16AU, I have 2 Year '10, 3rd week ones and year '10 33rd week ones. Only 3rd week ones are working good.

Did anybody made this V-USB based usb interface with an ATmega 8 manufactured in year 2011 as successful?

[DavidG]

Thank you for your reply.
I tried with many ATmega8 16PUs and ATmega8 16AUs.
Still I'm waiting for the answer from atmel, but some of users told me that they changed some silicon base format for newly made ones. I don't know even it does afffect a lot in electrical charicteristics or not.
But even with the poor designed circuit, if I'm using the same chip with same fusebits and same firmware then those should be working good anyway.
Only working good atmega with V-usb based circuit are newly made ones.
For ATmega8 16PU, I have year '06 made one and year '11 made ones(5 ones). only year '06 working.
For ATmega8 16AU, I have 2 Year '10, 3rd week ones and year '10 33rd week ones. Only 3rd week ones are working good.

Did anybody made this V-USB based usb interface with an ATmega 8 manufactured in year 2011 as successful?

Which one is the better one then here? I don't really get the difference.

[Peter Chaffe]

You didn't say what voltage your using!
You could be running on the edge of acceptance!

Using the 5v usb rail is out of spec for usb.
Reducing the voltage is bad for high clock speeds, and especially bad for overclocking.

I haven't been using v-usb for long but have done quite a bit of experimenting,
with a picky pc running xp! The results which work best for me are:

Drop the vcc rail voltage, either by using 2 diodes or vReg.
Use a 12mhz external crystal, it's better stability and lower freq than an internal osc running at 16.5mhz.

[Mike J.]

Every ATmega8 should work with 12MHz and 3.3V

I am working with ATmega8L-8 AU,
I have make a Test and they run with:
2.55V @ 12MHz (3.3V for V-USB, with 1k Ohm from +3.3V to D- , 1M from GND to D+ )
and
4.3V @ 26MHz (overclocking, 5V)

[Coda]

Yeah it would have been nice if the USB standard had used 3.3V at the supply or 5v on the signal rails, would have made hackers lives a lot easier

Back on topic, I concur with the observation above. However, for simplicity, ease, and for highest stability on every USB platform (mac/win/linux etc) with every AVR - unless you are building a project which is powered from 3.3v (maybe as part of a larger project which is 3.3v), I recommend running the mcu at 5v, (especially if you need >12Mhz), use 20Mhz parts (if there's no price/availability issue why buy 10mhz parts?) and use 3.6v zeners on the USB signal lines (like the BZX range), they are cheap and small. It would be nice if these AVRs came with accurate programmable high speed clocks built-in but that's a pipe dream lol.

[Micha]

Every ATmega8 should work with 12MHz and 3.3V

Maybe most of them will run, but be aware that they'll be out of spec and so there's no guarantee that they will do this under any circumstances. Only devices that are capable of 20MHz@5V will be in spec running with 12MHz@3.3V.