[Arm-netbook] RGB/TTL interface selection, why in EOMA-68

[jm]

On Thu, 2012-11-29 at 11:36 +0000, luke.leighton wrote:
> On 11/29/12, Henrik Nordström <henrik at henriknordstrom.net> wrote:
> > tor 2012-11-29 klockan 09:06 +0000 skrev luke.leighton:
> >> On 11/29/12, Tom Cubie <mr.hipboi at gmail.com> wrote:
> >>
> >> > The lcd is from BOE. The spec is here:
> >> > http://tom.linux-sunxi.org/hardware/datasheet/HV070WSA-100%20product%20spec%20rev.0%20%5b%e6%9c%80%e6%96%b0%e7%89%88%5d.pdf
> >>
> >>  superb!
> >
> > I wonder... maybe EOMA68 should already be revised to use LVDS instead?
> > Feels kind of stupid to have to do TTL->LVDS convertion when the CPU is
> > perfectly capable of delivering LVDS with just the flip of some software
> > bits.
> >
> > I kind of doubt there will be need for a CPU module based on a CPU that
> > can not do LVDS.
> >
> > But you know these things better than me.
> 
>  not necessarily!   but i have been over this, and nobody came up with
> an objection, the logic went as follows:
> 
> * EOMA_68 covers from as low as 320x240 all the way up to e.g. 2048x2048.
> * therefore whatever interface is chosen, it must NOT cause products
> which have 320x240 or even lower resolution LCDs to have to add 10%
> onto the BOM just for an LCD converter IC (whatever it is)
> * $1 for a converter IC when the BOM is $80 is however considered "acceptable"
> * therefore 24-pin RGB/TTL is pretty much the only
> lowest-common-denominator, lowest-cost option.
> 
> if you make dual-channel LVDS part of the standard as an "option", you
> just screwed absolutely every module provider whose SoCs do not have
> the capability to put both 24-pin RGB/TTL *and* dual-channel LVDS onto
> the same pins.
> 
> so, ridiculous as it seems initially, 24-pin RGB/TTL is the best
> option that i can see, when taking into account all the factors that
> i've been able to consider *so far*.
> 
> if anyone can come up with better reasoning it'd best be done quick
> because the A10 module is almost ready.

http://en.wikipedia.org/wiki/Low-voltage_differential_signaling
LVDS is differential signalling.
Its less noisy and less noise prone than parallel voltage buses.
Longer cables possible with LVDS.
My bet is that the future is likely to be LVDS and much lower power than
parallel buses.