Maxim has reduced slew rate rs485 transceivers which
work up to 250kbit/sec I think, and reflections or EMI
are greatly reduced in that way. Primitive
transceivers like 75176 have instead high slew rates
for being capable of transceiving 10mbit/sec for short
distances. Choosing ICs for the problem at hand will
give you best results.
Again if you see 32 as the max number of nodes low,
you can buy transceivers with 1/4 unit load (from
maxim), so you can connect in theory 128 nodes to the
bus.
is the ground dedicated to the communication as the
return path or do high power devices use that cable
for return too?
Murat Karadeniz
http://www7.brinkster.com/mukas
--- Reza <reza_agha@yahoo.com> wrote:
>
> --- Chuck Hackett <egroupscdh@WhiteTrout.net> wrote:
>
> > I would like to transfer data some distance (100
> > feet in one case, 400 feet in
> > another) between AVRs and I'm looking for the
> least
> > complex, least expensive way
> > to accomplish this. Environment:
> >
> > 1) Using facilities available on AVR processors
> > (such as UART, TWI, etc.)
> >
> > 2) I have cable in the ground which is Telco
> grade,
> > gel filled, direct bury
> > cable with 6 twisted pair
> >
> > 3) Speed is not critical. Of course I'd like to
> go
> > as fast as possible but I'm
> > willing to sacrifice speed to keep complexity/cost
> > down ... Well, I'd rather not
> > go back to the 110 bps days! :-)
> >
> > 4) Multimaster is desirable
> >
> > I'm thinking that the solution will use some king
> of
> > differential driver.
> >
> > I was doing some reading about TWI but it's
> unclear
> > to me if this works in this
> > situation. The only thing I could find about
> > distance limits was that the bus
> > capacitance must be below 400pf but I don't know
> the
> > capacitance of my cable ...
> >
> > BTW: I think this forum is appropriate for this,
> if
> > not, please let me know.
> >
> > Suggestions?
> >
> > Cheers,
> >
> > Chuck Hackett
> > "Good judgment comes from experience, experience
> > comes from bad judgment"
> > 7.5" gauge Union Pacific Northern (4-8-4) 844
> > http://www.whitetrout.net/Chuck
> >
> >
> >
> >
> Hi;
>
> as I know (using Siemens documents) if you use RS232
> (using MAX232) the distance is limited to 100 feet.
> but Siemens also offered some other solutions:
>
> signalling noise-prtction dist(feet) max-speed
> ----------------------------------------------------
> RS232 somehow 100 9600
> RS485 somehow 1500 9600
> RS422 good 3500 upto 19200
> CurrentLoop best 3500 max of 9600
>
> note: Siemens calls RS232 as V24, RS422 & RS485 as
> X27
> and CurrentLoop as TTY.
>
> in a very noisy environment the best solution is
> using
> current loop (4, 20mA) one node in Active (current
> generator) and the other in Passive (current
> switcher/detector) mode.
>
> but in steel making factory which I'm working, they
> use commonly RS422(Siemens:X27) in low noise
> environments, and CurrentLoop or TTY in high noise
> env.
>
> ofcouse you can make a network with these links. but
> for RS422/X27 there is a limitation of 32 partners
> on
> each link without repeater. for some applications
> see:
>
> www.rs485.com
>
> and see Texas Instruments products for RS422
> interfacing.
>
> otherwise if the environment is too noisy and you
> can
> pay more money, there is some fiber_optic-RS232
> switchs (eg: ADAM serias made by Advantech). or some
> wireless equipments (upto 20miles, with a speed of
> 115K bps) but is very expensive.
>
> good luck.
> (and excuse me for poor english!)
>
>
>
>
>
> __________________________________
> Do you Yahoo!?
> Y! Messenger - Communicate in real time. Download
> now.
> http://messenger.yahoo.com
>
__________________________________
Do you Yahoo!?
Yahoo! Mail - Helps protect you from nasty viruses.
http://promotions.yahoo.com/new_mail