[En-Nut-Discussion] Ethernut 2.1 + Using ports

[Harald Kipp]

m-c-m-c at gmx.de wrote:
> I am an beginner and want to use the Ports D0-D7 and A0-A14 from the expansion port not for data and adress-lines for memory! 
> I only want to use it as normal IOs and I don't need the ethernet, the memory controller and the SRAM from the board.
> Does I have to be aware of something if I do it?
>   
In general you can do so. Here's the schematic of the CPLD:

http://www.ethernut.de/pdf/enutcpld.pdf

In any case you need to make sure, that the external memory interface is
disabled. Nut/OS enables it in NutInitXRAM(), located in
nut/arch/avr/os/nutinit.c. This function will be excluded, if you remove
NUTXMEM_SIZE in the Configurator.
Disable RTOS Kernel -> Memory Management -> Extended Memory Size

This should make sure, that the read strobe is never triggered.
Otherwise the SRAM may activate its data bus lines.

As you already suggested, A15 should be excluded. I'd exclude all upper
4 address bits (PC4..PC7) and set them to high, except A12 (PC4), which
should be low. This will make sure, that none of the on-board chips ever
get selected.

Also note, that you are directly attached to several chips, when using
the memory bus lines. Electrostatic discharge or any overvoltage will
kill them all, not just the CPU.

Harald