20 years ago or so, I did what I called "absence of data token passing." Turns out the technique is also called "minislotted" time division multiplexing. This was done over a Bell 202 voice grade audio circuit. Our largest system had something like 15 nodes on 1,000 miles of circuit. It worked well as long as the circuit had low noise. The problem I have with token passing is the trouble you go to when the token gets lost (I believe "smashed" is the technical term). You can get a similar system without lost tokens by going minislotted. In my system (which, again, used modems on a voice circuit, so I had to deal with carrier detect times in the demodulators), each node was allocated 50 ms during which it could bring up carrier and start transmitting data. If a node had nothing to say, it would just not bring up its carrier. 50ms later, the next node would have permission to transmit. Each node had a "site counter" which kept track of whose turn it was. These site counters were all incremented 50ms after the last byte was received off the network (they would not advance as continuous data was being received). When a packet was received, all sites would set their site counters to the FROM address out of the packet, insuring they were all in synchrnonization. The system allowed for a maximum of 100 nodes (called sites in this system). Battery backed RAM held various network configuration settings. These included the number for this site, the highest site number (we would roll over back to site 0 after the site counters hit the max site - this sped up the system since it would not wait for nonexistant sites), and the "site delay" (the previously mentioned 50ms). The site delay could be changed if there were other delays in the network. This would typically happen if we used keyed UHF radios as the network path. The site delay would then be increased to 250ms to allow the radio receivers to break squelch. So, there are some thoughts on token passing.... By the way, this was all done using an MC6802 with code written in assembly using the Avocet 6800 cross assembler running on a Cromemco S-100 CP/M machine with two 8 inch floppies... Harold On Tue, 8 Jan 2002 11:04:50 -0300 Bob Dhios writes: > Hi Guys!!! > > Somebody knows as I can implement a token passing media access over > RS485 > with a 16F73? > > Thanx!!!! > > Bob > > -- > 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 > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. -- 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