AVR-Chat

RS485 bus connected devices share two cable (A,B), and
they communicate in a half-duplex manner, which means
while a slave or the master talks the others should
listen. You use a 75LS176 or equivalent RS485
transceiver ic with each slave. This IC contains a
receiver and transmitter, and you select which one is
active with the direction signal. the IC outputs the
A,B signals and you connect this outputs to a two
cable bus. The data is transferred as the voltage
difference between A, B and this brings great noise
immunity, since the aritmetic (A+noise)-(B+noise)
results in noise cancellation at microcontroller
datarates (100kbps) you can have a 1km bus.For more
information make a google search. I can provide you a
very efficient c source code if you need further help.

Murat Karadeniz



--- ckbanner <kcbanner@inbox.lv> wrote:
> HOw do I connect more than one mega8 slave to one
> master? I know rX
> and TX, but what do you mean by direction pin?  I
> thought serial prot
> was for connecting two micros together.  What do you
> mean by onboard
> comm?  
> 
> Thanks for the fast reply!
> 
> -Kc
> 
> 
> 
> --- In AVR-Chat@yahoogroups.com, MuRaT KaRaDeNiZ
> <karademu@y...> wrote:
> > mega8 has serial port, why not use RS485
> communication
> > bus. Single Master, multiple slaves (32 directly
> > supported, 128 possible with better driver ic's),
> > minimal IO requirements (TX,RX,direction pin). One
> > question however, are you doing onboard comm.?
> > 
> > Murat Karadeniz
> > 
> > 
> > 
> > --- ckbanner <kcbanner@i...> wrote:
> > > Hello,
> > > 
> > > I am doing a project where I need multiple mega8
> > > avrs sending sensor
> > > data to another controller.  The other
> controller is
> > > an OOPic-R.  The
> > > OOPic has built in functions for SPI, i2c(twi),
> and
> > > serial
> > > communications.  What is best for a multiple
> slave,
> > > single master
> > > system?  I can make code for the OOPic, but need
> > > some slave code for
> > > the avrs.  I am using Codevision and the help
> file
> > > doesn't have that
> > > much information about how to use i2c or SPI in
> > > slave mode.
> > > 
> > > Thanks,
> > > Kc
> > > 
> > > 
> > 
> > 
> > __________________________________
> > Do you Yahoo!?
> > Free Pop-Up Blocker - Get it now
> > http://companion.yahoo.com/
> 
> 


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