AVR-Chat

We are developing a monoriting system where I work. There will be 2 runs of
1000'. We are using "Mega Brain" boards from ERE http://www.ere.co.th . They
have ATMega128 and (2) RS485 ports. We will connect a MegaBrain to a server
via rs232 and connect to other MegaBrain's via rs485. We are going to use a
"MODBUS" protocall for our setup.

JoeT

-----Original Message-----
From: Chuck Hackett [mailto:egroupscdh@WhiteTrout.net]
Sent: Friday, October 29, 2004 3:07 PM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] Bus Distance



> From: Mike F. Schwarzer
>
> ....
> Look at the MAX485/MAX487 RS-485 Drivers, or if you like for DualTypes.
> With an RS-485 Bus, you can go up to 100M with 125kBaud, at
> least that was tested be myself.
>
> The Protocol depends on your Software, so its also possible
> to have Multi Master Access, from the AVR Side the simplest
> way is to use the UART.

Thanks Mike,

I've downloaded the datasheet and it looks like a winner.

I was wondering about how to be sure the ends of the bus are terminated so
as to
minimize reflections.  Is the best way to do this by connecting a scope
(mine is
100mhz) and driving the line watching for reflections and adjusting the
termination for minimum reflections, or am I
overcomplicating/oversimplifying
this?  I have no idea what the "characteristic impedance" of the cable in
the
ground is ...

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






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