Multi-drops on RS-485 network

[randyaz]

Jon,  I've started researching RS-485 and found out to use MAX485 transcievers and using Prop2's in a master/slave configuration. But I'm only finding bits and pieces of usable info and a great deal of "overwhelming" info so I'm finding it difficult to put it all together in realtion to the Prop2.  With the distances achieved and the inexpensive components the RS-485 network is intrieging...

Would you please give an overview of materials, connections, and maybe some sample code specific to RS-485 networking of, say,  3 Prop2s to flash LED's?



EDIT !!!

Geez...I shoulda known... I just came across your N&V columns.  Your da Man !!!

http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol2/col/nv55.pdf
http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol2/col/nv56.pdf

[JonnyMac]

I'm just getting into RS-485 myself (Lon wrote those other columns) having spent the last week working on my January N&V article and a project called SX-NET.  Here's the schematic for my project:

www.efx-tek.com/files/sx-net.pdf

And here's the board on my desk with a small serial-to-RS485 adapter:



Using the MAX489 allows the full-duplex comms, even if the Prop-2 can't handle that (the Prop-SX can).  Note that the DE line of the MAX489 allows the SX to have control of the RS-485 link when it's talking (only one device at a time should talk back to the master).  If you're using a half-duplex (or just one way) then the MAX485 [8-pin] chip will work.  I used that in the November N&V project that is "listen only."  The cool thing about the hardware is that it is transparent to the Prop-2 or Prop-SX.

Jan Axelson's book "Serial Port Complete" has a lot of good information.  The reason for my interest?  My friend, Peter, has network-controlled Halloween display (see www.socalhalloween.com).  My node, above, is hardware compatible with his system and I wrote a program that conforms to his protocol so my node works in his system -- this will let me build devices for his animation network next year.

[JonnyMac]

Here's a half-duplex circuit that minimizes the connections.  The cool thing about using the RS-485 stuff is that any device can "talk" to any other device -- you just have to come up with a protocol.

[randyaz]

geez...sorry Jon. I totally presumed those were your articles...  but your still da man!

[JonnyMac]

Thanks, Randy -- I'll have my network article in January.  And in case you want to get a preview of the article code, I've attached it; be warned, though, it's moderately complex.