Ben and Ethernet

Werner Almesberger werner at openmoko.org
Tue Aug 31 16:05:06 EDT 2010


Rikard Lindstr?m wrote:
> Maybe a micro controller could interface between SDIO and SPI (or
> other protocols), at least to free some CPU time.

As long as you only need bursts in one direction, letting the
external MCU treat (1-bit SD) like SPI might indeed be an option,
yes.

> I have a layout ready and uploaded on
> http://slashhome.se/p/uSD_breakout/ now. But it might be a bit hard to
> etch (0.2mm between the pads right now).

0.2 mm (8 mil) should be quite feasible with toner transfer. E.g.,
ben-wpan has a clearance of 8 mil. IDBG for the Ben even 7 mil.

I would run the rightmost trace parallel to its neighbour and not
so close to the board edge, though. Even the one on the left may
be a bit close. Since you're already dealing with a clearance of
8 mil at the pads, there's no reason why you'd have to go to much
wider spacing at the traces.

- Werner




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