[En-Nut-Discussion] Ethernet HW questions

[Henrik W Maier]

Hi!

Just received my Ethernut 1.3F evaluation kit and I am very excited 
with the quality of soft and hardware. Great job.

I am currently designing a custom hardware based on the Ethernut 1.3 
design and like to do a couple of minor changes. Maybe somebody has 
already done this and wants to comment.

A) Power-on reset generation
I like to remove the DS1811 and replace it with a simple RC 
combination like many other AVR designs do. Isn't the DS1811 anyway 
redundant because of the ATmega's internal brown-out detection?

B) RTL8019AS reset pin
I like to connect the reset to an AVR port to save the need for an 
inverter gate.

C) RTL8091AS interrupt pin
This pin can be connected directly to the ATmega128 to save an 
inverter gate. I assume the inverter was only necessary for the older 
ATmega103 chip which didn't have programable interrupt levels.

D) RTL8091AS half-duplex mode
I also like to connect pin 77/EEDO/BD7 to ground to force the RT into 
half-duplex mode. This was suggested by RealTek's support. In this 
case LED_BNC has to be used to indicate the Link status as the LED 
configuration cannot be changed by the cfg registers. I have seen the 
LED_BNC solution in some other reference designs supplied by RealTek 
and also tested it using the PacketWhacker.
When grounding pin 77/EEDO/BD7, the JP pin 65 can then be left open 
so the RealTek operates in "RT jumperless mode".

E) Realtek 270R pulldown resistors on pin 48,49
Aren't these rsistors obsolete because AUI is not used?

F) /RD, /WR, ALE signals
These signals are floating in reset or if the ports are not 
configured. Shouldn't they have pull-up resistors?

G) AVCC/AGND/AREF
I won't need analogues on the board. What's the best way to deal with 
these supply signals? Connect them to VCC and GND or leave them 
simply open?

H) RTL8091 address signals
I like to use only the A0 to A4 and A8 (connected to ATmegas A15 as 
chip select) address signals on the RealTek. A9 is pulled high all 
other address signals low. This results in the RealTek occupying the 
whole upper 32K address space.
Doing this I need less tracks to route and I save the inverter gate 
for A15. 

Cheers,
Henrik