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Great! That really helps me.
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<p>By the way: In the pinouts table on <a moz-do-not-send="true"
href="http://t224.mjt.lu/lnk/AEQAG_j9MacAAAAAAAAAAGbE2wkAASHlFNUAAAAAAAZHgABYYlyWy1rDqWHDQDSaTthYM5vW_AAGAjk/1/p4fGNCiVfzJ3eH2UJ5KwKA/aHR0cDovL2VsaW51eC5vcmcvRW1iZWRkZWRfT3Blbl9Nb2R1bGFyX0FyY2hpdGVjdHVyZS9FT01BNjgvSGFyZHdhcmU">elinux.org</a>
(<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://t224.mjt.lu/lnk/AEQAG_j9MacAAAAAAAAAAGbE2wkAASHlFNUAAAAAAAZHgABYYlyWy1rDqWHDQDSaTthYM5vW_AAGAjk/2/X2GdNs5QKh19NWGQD45vDw/aHR0cDovL2VsaW51eC5vcmcvRW1iZWRkZWRfT3Blbl9Nb2R1bGFyX0FyY2hpdGVjdHVyZS9FT01BNjgvSGFyZHdhcmU">http://elinux.org/Embedded_Open_Modular_Architecture/EOMA68/Hardware</a>)
there are duplicate signals on pins 27 and 28, I am pretty sure
that pin 27 was meant to be SSRX- instead of SSTX-.</p>
<div class="moz-cite-prefix">On 27.12.2016 05:23, Luke Kenneth
Casson Leighton wrote:<br>
</div>
<blockquote
cite="mid:CAPweEDywFK1A+22coQQJBO3Nt1qyxmxbAYMb30sOOamVhjyhJg@mail.gmail.com"
type="cite">
<pre wrap="">---
crowd-funded eco-conscious hardware: <a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://t224.mjt.lu/lnk/AEQAG_j9MacAAAAAAAAAAGbE2wkAASHlFNUAAAAAAAZHgABYYlyWy1rDqWHDQDSaTthYM5vW_AAGAjk/3/tTv2eaJ4e59FsHrl8usbXA/aHR0cHM6Ly93d3cuY3Jvd2RzdXBwbHkuY29tL2VvbWE2OA">https://www.crowdsupply.com/eoma68</a>
On Mon, Dec 26, 2016 at 6:00 PM, Internet <a moz-do-not-send="true" class="moz-txt-link-rfc2396E" href="mailto:internet@devpi.de"><internet@devpi.de></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hey, I am planning a custom project utilizing the EOMA68 standard
</pre>
</blockquote>
<pre wrap=""> cool!
</pre>
<blockquote type="cite">
<pre wrap="">and I was wondering about VREFTTL.
</pre>
</blockquote>
<pre wrap=""> ya.
</pre>
<blockquote type="cite">
<pre wrap="">What I have read so far (elinux.org) is that VREFTTL refers to the
maximum voltage that can be applied to the GPIOs. My questions are
though: Is VREFTTL always 3.3V
</pre>
</blockquote>
<pre wrap=""> *NO* it's not.
</pre>
<blockquote type="cite">
<pre wrap="">or can it be lower?
</pre>
</blockquote>
<pre wrap=""> between 1.8 and 3.3v, at the moment. anything lower will need to be
negotiated in a FUTURE standard (and the "default" range of 1.8v to
3.3v will be respected, for older Housings. that means SoCs will need
to have variable voltage power domains, but that's actually becoming
quite common.
</pre>
<blockquote type="cite">
<pre wrap="">What should I do, if
some ICs require a certain supply voltage
</pre>
</blockquote>
<pre wrap=""> please do NOT make the mistake of using VREFTTL as a *SUPPLY*
voltage. most (complex-function) ICs have a VDD (digital supply
voltage) and a VCCIO. the VCCIO is what you connect to the VREFTTL.
take a look at the SN75LVDS83b or the TFP401a for examples.
</pre>
<blockquote type="cite">
<pre wrap="">and VREFTTL does not meet the
requirements?
</pre>
</blockquote>
<pre wrap=""> find another IC that meets the variable-voltage 1.8 to 3.3v CMOS
reference voltage or do level conversion.
</pre>
<blockquote type="cite">
<pre wrap="">Would it be necessary do level shifting in advance (to be
compatible with other voltages)?
</pre>
</blockquote>
<pre wrap=""> yyep. there's a number of ways to do it, dozens of ICs and circuits:
the TXS0104 is great because it supports both open drain and
push-push, you can use a MOSFET, or in some cases a straight diode
will do (in a really counter-intuitive way, but it works). take a
look on the rk3288 schematic PDF, look for the HDMI page, you'll find
a suitable converter circuit using a MOSFET (and protection diode).
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://t224.mjt.lu/lnk/AEQAG_j9MacAAAAAAAAAAGbE2wkAASHlFNUAAAAAAAZHgABYYlyWy1rDqWHDQDSaTthYM5vW_AAGAjk/4/yUD5jmRyfDBXLDKESf-haQ/aHR0cDovL2hhbmRzLmNvbS8lN0Vsa2NsL2VvbWEvcm9ja2NoaXBfcmszMjg4Lw">http://hands.com/~lkcl/eoma/rockchip_rk3288/</a>
l.
</pre>
<blockquote type="cite">
<pre wrap="">How much current can I draw out of the
computing card?
</pre>
</blockquote>
<pre wrap=""> up to around 300mA. do *not* go beyond that.
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