--- crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
On Fri, Jan 12, 2018 at 11:37 PM, Richard Wilbur <[email protected]> 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 <[email protected]> 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 such decisions. 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 makes sense. l. _______________________________________________ arm-netbook mailing list [email protected] http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to [email protected]
