Re: gEDA-user: flash data bus pinout

[asomers@xxxxxxxxx]

It should work fine, but remember to write a script that bit flips
your PROM image too.

As for SDRAM, there are a few gotchas.  First, what is the width of
your SDRAM?  If it's 8-bits wide, then you're golden.  But if it's
wider, then you need to remember that SDRAM can be accessed 8, 16, or
32 bits at a time.  In a 16-bit chip, there should be two pins (DQL
and DQH or something like that) that control which bytes get written
during a write operation.  When you decide how to route the data
lines, you should trace out in your mind all possible combinations of
those pins (write low byte, write high byte, write both bytes for a
16-bit chip) and make sure that the right combination of bits gets
recorded.

For example, with a 16-bit chip, you could scramble the lower 8 data
lines amongst themselves, and the scramble the upper 8 amongst
themselves.  Or you could swap the lower 8 lines with the upper 8, but
then you'd have to also swap the DQL and DQH lines.

That all assumes that you have just a single SDRAM chip.  If you have
multiple chips, you'll need to consider their CS pins too.

Good luck.

-Alan

On Wed, May 5, 2010 at 7:41 PM, gene glick <carzrgr8@xxxxxxxxxxxxx> wrote:
> I have an 8-bit flash PROM to connect to a uP.  It's the only PROM.
> Otherwise the micro data bus is 32-bit wide, and SDRAM lives there.  The
> PROM has it's own CS, ALE, etc.  For a better layout, it would be far
> easier to route D0 of the uP to D7 of the PROM.  I don't see any reason
> not to - just wondering if you all agree.  This is something I've done
> in the past with SRAM, but heard it's not kosher with SDRAM.
>
>
> thanks
>
> gene
>
>
>
> _______________________________________________
> geda-user mailing list
> geda-user@xxxxxxxxxxxxxx
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>


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