[En-Nut-Discussion] Ethernut 2

[Harald Kipp]

Hi Douglas,


>I am redesigning an EtherNut 1.3 daughter board (Quad UARTS, 
>RS485/232/IrDA/Flash RAM, RTC clock/calendar, etc etc) to work with the 
>newer EtherNut 2.

I've done everything to make this as painless
as possible.


>As I am not sure my previous posting got through, I d like to summarise my 
>questions about the EtherNut 2:

The mailing list was down. Took a few
days (and hints from kind people) to
detect this problem.


>PE6 (INT6) is NOT used and can by used by my own design.

PE6 is not used. In fact, Ethernut 2 may use more
Port Bits than Ethernut 1, but this is all optional
and jumper selectable.


>Only RESET\ and not RESET goes to the expansion header (any plans to 
>change this???)

No, there are no plans to further change the
Ethernut Expansion Connector. Take Ethernut 2
as final...

OK, if we change this, there will be jumper. :-)



>I can use 0xFE00 0xFEFF to memory map my own design (if not, what ranges 
>are available?).

0xFFXX is the bank select register. However, this
is decoded in the CPLD and can be changed.

I'll publish an Ethernut application to reprogram
the CPLD soon. No need for a Xilinx JTAG adapter.

Also the LAN91C111 address is decoded in the CPLD
and thus changable. It currently located at 0xC000.

We intentionally put the SMSC Controller at the
beginning, so the upper regions are kept available
for slower hardware. Remember, that the ATmega can
specifically add memory cycles on upper regions.

I'd suggest to use 0xDXXX for extension without
waits and 0xEXXX for slow hardware.


>And lastly, the daughter board can draw at a peak, 5v up to 1.7 amps.

That's a lot.


>In the past, the daughter board has a 5v 3A power supply that supplies the 
>5v to the EtherNut 1.3 via the expansion header (we remove the 5v 
>regulator from the EtherNut).

Yes, the Ethernut 2 isn't still perfect. An additional
diode bridging the 5V regulator would avoid to have it
removed...sigh.

But why not supply the DC pin with unregulated power
(Expansion pin 10)?


>Is it possible to upgrade the LM1086(1.5A) to a LM1085 (3A) or a LM1084(5A)?

Sure, that was one reason why I chose this somewhat
exotic regulator. However, your input voltage should
be as low as possible, luckily LM108x are LDOs. 6.5V
may already work, 7V is stable and fine.

Using higher input voltages will produce a lot of
heat with 1.7 Amps. And Ethernut 2 already becomes
quite warm because of the 100 MBit controller.

But the major problem are the traces and the rectifier
bridge. Theoretically the unregulated DC trace width is
sufficient for 1.85 Amps only, but they may already warm
up. Worse, the rectifier takes 800 mA max. They are
available for 1 Amp, but I do not know about any higher
current.

The 5V traces are no problem because Ethernut is a four
layer board and has it's own supply layer, directly
connected to the expansion port.


>What else would need to change (F1 to 3A or 5A)?

Right, the fuse needs to be changed.


>Would this work with the current board design (track width, vias etc)?

If there are just _peaks_ of 1.7 Amps, changing
the regulator, replacing the fuse and shorterning
the rectifier should work. But it depends on what
you name peaks and how often they may occur or
what's the average current. It's mainly a heat
problem and thus depends on the environment.



>I guess this will become more of an issue as more and more daughter / 
>expansion boards are developed!

The few power hungry boards we designed got their
own regulators and used the DC pin to supply Ethernut.
This design has a better heat distribution.


>The other alternative is to put a LM1084 on the daughter board, and 
>removing the LM1086 from the EtherNut, which would not be my preference.

See above.

Harald