Date: Sat, 17 Feb 96 21:14 WET From: uhclem@nemesis.lonestar.org (Frank Durda IV) To: hackers@freebsd.org Subject: Re: Multidrop serial (422/485) driver Message-ID: <m0tnzaS-000C8oC@nemesis.lonestar.org>
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[0]The 'mdsio' driver provides support for multidrop serial busses, either [0]using a standard RS-422/485 interface card, or a standard RS-232 serial [0]port with DTR- or RTS-controlled transmit/receive. [2]Jordan K. Hubbard stands accused of saying: [2]Uh. Interesting. I wasn't aware that anyone was still playing with [2]serial networks since they dismantled BERKNET. :-) [2] [2]Are you guys actually using this stuff in such an application? [3]It's called "industrial control". RS-485 is very heavily used in [3]machine interfaces; properly wired it's nearly immune to interference, [3]you can run it hundreds of metres over telephone cable, and it takes a [3]$0.75 part to interface it to almost any UART or microcontroller. Yes indeed. Someone in my office was complaining that their group has a bunch of Betacam SP transports that they drive into the ground by doing frame-at-a-time record and sample. They sit there and rewind, roll, record one frame, rewind, roll, record one frame, all day long. They want to do batch record and batch playback, but they have to use the 422 interface on the deck for this. However the drive package for DOS costs several hundred for RS-232 decks and an extra $1K for the modules for driving 422 decks. He was looking for drivers for *any* platform.... Hmmmm... Also, there are several HVAC systems that use RS485 to poll temperature sensors, activate boost heaters and blowers, and generally control things. I know of a seven story building in Ft. Worth TX wired with such a system that was bought off the shelf. And, if you are so inclined, Appletalk is really 485 running at 230.4Kbit/sec over a somewhat strange wiring arrangement. Centram/Farallon use the same scheme (and unshielded wire for triple the network size) and bump the speed to 230.4K or 768K, and Tandy copied the Centram design (down to the jumper numbers) and sold it as TandyLink. Those Tandy cards are driving a lot of DOS packet radio equipment all over the place, and are cheap. Frank Durda IV <uhclem@nemesis.lonestar.org>|"The Knights who say "LETNi" or uhclem%nemesis@rwsystr.nkn.net | demand... A SEGMENT REGISTER!!!" ^------(this is the fastest route)|"A what?" or ...letni!rwsys!nemesis!uhclem |"LETNi! LETNi! LETNi!" - 1983
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