[En-Nut-Discussion] Memory Question

[Michael Baverso]

Thanks for the reply.....

----- Original Message -----
From: "Alastair Jeremy" <ajeremy at dotaussie.com.au>
To: <en-nut-discussion at egnite.de>
Sent: Thursday, December 19, 2002 4:40 PM
Subject: RE: [En-Nut-Discussion] Memory Question


> Hi Mike,
>
> Short answer: no. (I assume you are talking about on the Ethernut)
>
> Long answer: The ATmega itself always just "looks for" the exact specified
> address, using a 16 bit databus (assuming you haven't changed the register
> which reduces the number of high bits in the address). If you want to
access
> the lower 4kb or so then there are two ways of achieving this: one is to
use
> the method in the ATmega datasheet, and the other is to have a complex
> external decoding mechanism which "converts" a particular range of
addresses
> to actually address the lower 4k of SRAM.
>
> The Ethernut does not have this complex external decoding mechanism. It
just
> uses the A15 line to select the SRAM or not. So since between 8000-82ff
A15
> will be high, the SRAM chip will not be selected. If you had some way of
> making -CS on the SRAM be asserted during this range, then the addresses
> would wrap around like you suggested. Reducing the number of 'upper
address
> lines' as per the ATmega datasheet would work (and setting -CS asserted
all
> the time for the SRAM), but then you would lose the ethernet controller.
>
> Alastair Jeremy
> DOT AU Pty Limited
> http://www.dotaussie.com.au/
>
>
> -----Original Message-----
> From: en-nut-discussion-admin at egnite.de
> [mailto:en-nut-discussion-admin at egnite.de]On Behalf Of Mike Baverso
> Sent: Friday, 20 December 2002 4:05 AM
> To: en-nut-discussion at egnite.de
> Subject: [En-Nut-Discussion] Memory Question
>
>
> Ref: ATMEGA128 datasheet page 31 'Using all Locations of External Sram
> Smaller than 64K'
>
> Do addresses 0x8000-0x82FF map directly to 0x0000-0x02FF of the sram???
>
> Regards,
>
> Mike Baverso
> Elcon Technologies, Inc.
> 106 Rochester Road
> Pittsburgh, PA 15229
>
> Phone:412 931 8250
> Fax:    412 931 8254
> Cell:    412 559 4865
> mbaverso at elcontech.com
> www.elcontech.com
>
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