[En-Nut-Discussion] Ethernut 5.0 Schematic Preview

[Harald Kipp]

Alain M. wrote:
> 
> 1) have you considerd powering the ATMEGA with 3.3V, I believe that a 
> LOT of things would be simpler. In fact I have ben studying a project 
> very similar to that (ARM9 + AVR for supervion) and I noticed that it 
> runs very well at 8MHz with 3V3. A lot of level shifts would be 
> eliminated :)

Then we either need another 3.3V regulator or the ATmega won't be able 
to switch off the 3.3V supply. See below.


> 2) I supose that L1, L2 and L4 are there for EMI too?

Yes, these are common mode chokes. Using RC filters on high speed USB 
may not work.


> 3) dividers R67/R63 and R69/R65 are somewhat strange, wouldn't it be 
> just a simple pull-up?

Several parts are optional but not yet marked as such. Decisions will be 
made when playing with the prototype. It is helpful to have the pads 
available. Also, some of the level shifters are not really required.


> 4) if you have a RTC chip, you should have a battery too... it could on 
> the bottom side of the board so that it does not use any pcb area, or at 
> least justa connector could be nice.

Mounting a battery on the bottom side would require manual soldering. 
Beside that, the board may not fit in the same place as used for other 
Ethernuts. C11 may be increased to 0.33F. As this is a through hole 
part, you may attach an external battery (plus a diode) the the pads 
instead.


> 5) F1 could be a Polyswitch, more practical, uses much less board space.

This had been proposed several times for the other Ethernuts as well. 
IMHO, a TVS in conjunction with a fast acting fuse is the safest way to 
avoid all kind of problems. If the fuse blows, something went miserably 
wrong and it's good to force someone to look to it before replacing the 
fuse.


> 6) This is going to be a Develloper's tool, so IMHO no pin should be 
> unreacheable (TST, SHDN, A18, A19, A20 maybe more...)

Mh, well, not really. The majority of Ethernuts are used in real 
equipment. And, as stated previously, we try to maintain compatibility 
among board versions, so the connectors are limited. I doubt, that 
someone will ever miss these address lines.

However, while doing the board layout, we will add a few test points for 
our test adapter. Note, that pins 63 and 64 are left unconnected on all 
Ethernuts.

The Elektor Internet Radio was mainly done as a developer board and thus 
we decided not to use a different layout.


> That is about it :)

Many thanks, Alain.

> PS, consider the JTAG standard connector once more...

:-) I didn't feel that this discussion has ended yet.


Harald