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So after a weekend and some playing with gEDA and pcb (learning
curve that was) I drew up a schema [1] from what we talked about
earlier.<br>
<br>
After spending some hours routing I decided to make a second version
(there is plenty of room on a 5x5 pcb) with the header in the
middle, instead of the edge and thus a 2 design PCB was born [2].
Before I send this off to the PCB fab and have some boards made, I
was hoping what you guys thought and whether it is sound. I've
attached a more or less 'complete' render [3] and one without the
silkscreen [4] (probably most usefull).<br>
<br>
(M)any pointers appreciated, this being my first board ever designed
:)<br>
<br>
[1] dspif_sch.png<br>
[2] dspif_photo.png<br>
[3] dspif.png<br>
[4] dspif_nosilk.png<br>
<br>
On 03/07/12 16:28, Oliver Schinagl wrote:
<blockquote cite="mid:4F577EBB.7000305@schinagl.nl" type="cite">On
06-03-12 19:33, Peter Stuge wrote:
<br>
<blockquote type="cite">Oliver Schinagl wrote:
<br>
<blockquote type="cite">Pin 1, 'chip select enable' is an
inverted? pin. enables and
<br>
disables device operation. When chip select is high, the
device is
<br>
de-selected and the serial data pins are at 'high impedance'.
<br>
</blockquote>
Correct.
<br>
<br>
<br>
<blockquote type="cite">So if I understand all this correctly,
the chip can be
<br>
connected in parallel with the exception of the Chip Select
Enable.
<br>
A simple switch to either connect it directly to the
<br>
board/socket/other end and toggle it to connect to ground (via
<br>
'some' resistor').
<br>
</blockquote>
Right. This is what you can see demonstrated in the photos
linked to
<br>
at the bottom of <a class="moz-txt-link-freetext" href="http://stuge.se/m57sli/">http://stuge.se/m57sli/</a> i.e.:
<br>
<br>
<a class="moz-txt-link-freetext" href="http://stuge.se/m57sli/overview.jpg">http://stuge.se/m57sli/overview.jpg</a>
<br>
<a class="moz-txt-link-freetext" href="http://stuge.se/m57sli/U5.jpg">http://stuge.se/m57sli/U5.jpg</a>
<br>
<a class="moz-txt-link-freetext" href="http://stuge.se/m57sli/U9.jpg">http://stuge.se/m57sli/U9.jpg</a>
<br>
<br>
These photos are not from a PC mainboard but the principle
hopefully
<br>
shows. The connection you describe is indeed how GIGABYTE boards
<br>
implement Dual BIOS. What is not shown in my photos are the
<br>
resistors, which are mounted onto the GIGABYTE board on pads for
that
<br>
very purpose.
<br>
</blockquote>
After this mail-conversation, those images make perfect sense!
<br>
<blockquote type="cite">
<br>
<br>
<blockquote type="cite">I tried to make a simple schematic in
ascii, but failed horribly so i've
<br>
attached it to this message as monochrome BMP (only format
that I could
<br>
quickly think of to be smallest in size).
<br>
</blockquote>
Hint: png
<br>
</blockquote>
I thought I tried and came out to 54kb, I redid them in this new
version and it is only 998 bytes! Nice!
<br>
<blockquote type="cite">
<br>
<br>
<blockquote type="cite">I don't know what value those resistors
need to be (and if the
<br>
schematic can be even more simplified, with a single
resistor), but
<br>
I belive this is the schematic used for the dual-SPI flash
'module'
<br>
</blockquote>
Not quite, the resistors need to be pull-up and not pull-down.
See
<br>
e.g. <a class="moz-txt-link-freetext" href="http://stuge.se/flash_switch.png">http://stuge.se/flash_switch.png</a> which shows the principle
with
<br>
resistors, but connects the switch common to GND, instead of to
the
<br>
mainboard as must be done.
<br>
</blockquote>
Hmm, I made a new 'design' and I put the common of the switch to
the GND, but you say it should connect to the motherboard? Why is
this?
<br>
<blockquote type="cite">
<br>
<blockquote type="cite">This seems sensible to me, but my
knowledge in
<br>
this field is very limited.
<br>
</blockquote>
You're already learning more. Your schematic is correct, but
<br>
resistors need to pull up to 3.3V and not down to GND. The
values
<br>
are, as I wrote earlier, not really critical, just don't go too
<br>
much under 1k or you will potentially waste some current.
<br>
<br>
Also make sure that your switch is the break-before-make type.
<br>
</blockquote>
Learn I did, I'll now try to learn some gEDA and design a basic
PCB for this purpose!
<br>
<blockquote type="cite">
<br>
//Peter
<br>
<br>
</blockquote>
<br>
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<br>
</blockquote>
<br>
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