[Arm-netbook] Crowsupply update
Luke Kenneth Casson Leighton
lkcl at lkcl.net
Sat Jan 13 01:15:35 GMT 2018
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
On Fri, Jan 12, 2018 at 11:37 PM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:
> Last time I asked these questions I succeeded in hiding them in the middle of a bunch of other text.
> On Jan 9, 2018, at 06:26, Richard Wilbur <richard.wilbur at gmail.com> wrote:
>> What kind of logic are these GPIO pins? (CMOS, TTL, etc.)
> The type of logic determines the input and output voltage and current
> source and sink characteristics (both capabilities and expectations).
> Do you have the Allwinner documentation for the A20--specifically for
> the GPIO pins?
ok google "allwinner a20 datasheet" or better "allwinner a20
reference manual" you'll find it.
>> So there are 4 pairs or 8 GPIO lines to test? (I thought we
>> had more lines dedicated to GPIO and two more that were
>>going to be used as I2C for VGA? Are only 8 easy to test?)
the choice - on the Microdesktop PCB - to arbitrarily utilise two of
the GPIO pins as bit-banged I2C - is entirely one that is legitimate
yet has absolutely nothing to do with the EOMA68 specification,
*other* than, "It Is Permitted" under the EOMA68 specification to make
the choice - on the Microdesktop PCB - to arbitrarily utilise those
two GPIO pins as bit-banged I2C - is done because the termination
impedance for VGA EDID is, according to the specification, somewhere
around 10 kOhms, whereas the normal I2C termination resistance is
usually somewhere around 2.2kOhms.
i felt therefore that it was important *not* to have the VGA I2C
lines connected to the EOMA68 I2C bus.
these decisions have *nothing to do with the EOMA68 specification*,
they are simply "permitted under the EOMA68 specification" if that
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