Great! That really helps me. By the way: In the pinouts table on elinux.org <http://elinux.org/Embedded_Open_Modular_Architecture/EOMA68/Hardware> (http://elinux.org/Embedded_Open_Modular_Architecture/EOMA68/Hardware) there are duplicate signals on pins 27 and 28, I am pretty sure that pin 27 was meant to be SSRX- instead of SSTX-.
On 27.12.2016 05:23, Luke Kenneth Casson Leighton wrote: > --- > crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68 > > > On Mon, Dec 26, 2016 at 6:00 PM, Internet <[email protected]> wrote: >> Hey, I am planning a custom project utilizing the EOMA68 standard > cool! > >> and I was wondering about VREFTTL. > ya. > >> 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 > *NO* it's not. > >> or can it be lower? > 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. > > >> What should I do, if >> some ICs require a certain supply voltage > 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. > >> and VREFTTL does not meet the >> requirements? > find another IC that meets the variable-voltage 1.8 to 3.3v CMOS > reference voltage or do level conversion. > >> Would it be necessary do level shifting in advance (to be >> compatible with other voltages)? > 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). > > http://hands.com/~lkcl/eoma/rockchip_rk3288/ > > l. > > > >> How much current can I draw out of the >> computing card? > up to around 300mA. do *not* go beyond that. > > _______________________________________________ > arm-netbook mailing list [email protected] > http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook > Send large attachments to [email protected]
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