AVR-Chat

Robert wrote:
> Why don't you use I2C to link to other microprocessors? It's more
> effective, no termination problems to deal with.
> 
> Robert
> 
>>> I am using a micocontroller to communicate with 18 other 
>>> microcontrollers via rs489. Using the IC MAX3088, and a 100 ohm 
>>> resistor across A and B.. Since there are 19 MAX3088, there are also 
>>> 19 100 ohm in parallel. IS there something wrong with this? the 
>>> resulting resistance is only about 5.3 ohms. 
>>>   


rs485 has a lot better noise immunity and only needs 2 or 3 wires(+power).
see http://www.circuitcellar.com/library/ccofeature/perrin0799/c79bp3.htm

With the latest transceivers can run at up to 16Mb on short range (10 - 
50m) or at 100Kbps or slower for up to a few km.
Over 1km/4000ft you may need to insert repeaters in the line.

A project I was working on and may be again
(I find out tomorrow) is a bridge vibration monitoring system.
We can connect all the sensor boards(4 - 8) via rs485 in each string 
with a single cable - 6 core twisted shielded cable.
Looking at using around 100kbps per string approx 64 or 120 feet long.

Usually avoid using maxim parts because they can be quite
hard to get in the quantities you want at decent pricing but
for rs485 they are the best!

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4631

The max13088 which he  is using allows up to 16Mbps(10 - 30m)
and up to 256 transceivers on the bus.

Nice thing is they are still available in dip.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/2116


Could also use can bus for longer distance comms where you can't use 
ethernet. The new airbus and beoing aircraft even use can over tcpip
for flight controls and enginer controls.
arinc 629 , 664 if you want more details.

http://www.aviationtoday.com/av/categories/military/1198.html

Alex