I have a curcuit that utilitizes a full-duplex, multi-drop 485 network with collision detection/avoidance. I could forawrd you a copy if you'd like... Douglas Wood Software Engineer dbwood@kc.rr.com Home of the EPICIS Development System for the PIC and SX http://epicis.piclist.com ----- Original Message ----- From: "Byron A Jeff" To: Sent: Sunday, July 22, 2001 3:10 PM Subject: Re: [PIC]:Thoughts on RS485 collision detection > On Sun, Jul 22, 2001 at 02:17:55PM -0400, Brandon Fosdick wrote: > > Chris Carr wrote: > > > > > > I have only been half following this thread so my apologies if I have got > > > hold of the wrong end of the stick. > > > > > > I have implemented a somewhat similar system on RS485 using a Slotted Aloha > > > Protocol. It works very well on low throughput systems and is quick and > > > cheap to implement. > > > > > > I was originally going to use CAN for the system and even invested in a > > > MCP2510 Development Kit. Only then did we get the Standards and when we > > > started reading them it slowly became clear that CAN is only a transport > > > media same as RS485 (except it includes error checking, collision detection > > > etc etc) You still have to overlay it with a Communications Protocol. The > > > idea of using CAN was rapidly dropped as the complexity could not be > > > justified for that project. > > > > I'm not familiar with Slotted Aloha, can you provide more details? > > That's what search engines are for. I plopped slotted aloha into google and > 10 pages of entries popped out. > > It's a collision detection system that forces each node to transmit on an > agreed upon boundary with fixed message sizes. In this way collision detection > can be guranteed because multiple transmitters will all transmit at the same > time. > > The only question I had is how does EIA-485 transceivers guarantee reports of > collisions? I thought that multiple transmitters on the bus would not guarantee > a known state on the line. > > BAJ > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics