[En-Nut-Discussion] How Ethernut 1.3-Rev. G hardware works?

[Janusz U.]

> Ok, I'm trying to understand. For me, the external RAM is not avaible, 
> it's
> in deselected mode, when CE/ is high, so when A15 pin is high (cf.
> functional description in the DataSheet). At the same time, the RTL's pin
> SA15 is at low. Because :
> A15 = H
> so CE/ = H => External RAM not enabled
> A15 is inverted so SA15 is LOW.

exactly, RAM is deselected for 0x8000-0xFFFF

> It's not logical :( ! Where am I wrong? They are enabled at the same 
> time...
RAM is disabled by CE/ - only RTL is enabled because

> 0x8000 = 0b1000/0000/0000/0000 => only A15=1
> 0x8300 = 0b1000/0011/0000/0000 => A15=A9=A8=1

RTL has an INTERNAL ADDRESS DECODER for address range 0x0300-0x031F. 
Therefore A15 is inverted...

I hope this helps you
Janusz