tac@sei.cmu.edu (Timothy Coddington) (07/29/88)
Would someone please take the time to compare the basic differences between the standards: RS-232, RS-232C, RS-485, and RS-422. I would suspect they differ in max data rates, type of transmission, signals, and protocol. RS-232, and RS-232C probably don't differ that much with respect to the attributes I'm listed, but what is the difference ? Also, if you are aware of what dictates using one over another, please mention that too. Are there others like this I've missed that fit in this class of interface, and is a standard? Thanks for taking the time. Tim Coddington arpanet: tac@sei.cmu.edu Software Engineering Institute, CMU 412-268-7712 ps If I get what I think is a comprehensive list I'll post to the net.
henry@utzoo.uucp (Henry Spencer) (08/03/88)
In article <6436@aw.sei.cmu.edu> tac@sei.cmu.edu (Timothy Coddington) writes: > Would someone please take the time to compare the basic > differences between the standards: RS-232, RS-232C, RS-485, and > RS-422... Okay, since nobody else has tackled this one in public, I'll try... RS232 Usually a synonym for RS232C, the most modern version of RS232. RS232B and its predecessors are so ancient that they're quite irrelevant nowadays. RS232C Widespread standard. Positive and negative voltages, usually +-9 or +-12, which is a pain for modern +5 equipment. Fairly slow, peters out around 50kb. Fairly short-range, the rules say 50 ft maximum, although one can often get away with fairly major violations of this. Gross-overkill 25-pin connector, of which only about 10 pins ever get much use. Signalling conventions designed for connecting modems to terminals, widely ignored and abused in various obscene ways due to carelessness, ignorance, and (sometimes) needs not anticipated in the original standard. RS422 Differential signalling at +5. Needs twice as many wires as the single-sided standards, but the payoff is much higher speed and longer range, with megabit rates possible over hundreds of meters. Much used in low-end local networks etc. There is a separate standard, RS339 or something like that I think, defining things like connectors and signalling conventions; by and large it's so silly that nobody pays any attention to it (would you believe a 37-pin connector, supplemented by an auxiliary 9-pin connector?!?). RS423 Intended as a replacement for RS232. +-5 volts to make it easier for modern equipment, and electrical specs cleaned up to permit higher speeds (100s of kb) over modest distances. More or less compatible with RS232. Not too widely used, and much of the incentive for it has gone away with the Maxim chips (which handle the voltage generation for RS232). (Everybody uses 422 for the fast stuff anyway, so 423's greater speed buys little.) RS485 If I've got this straight -- I don't know much about this one -- this is RS422 with small improvements to make it more useful for "party line" systems like small bus-oriented local networks; in particular, the transmitters have to be tough enough to stand having at least one other transmitter live on the wire at the same time. -- MSDOS is not dead, it just | Henry Spencer at U of Toronto Zoology smells that way. | uunet!mnetor!utzoo!henry henry@zoo.toronto.edu
tmk@io.ATT.COM (59481[rjb]-t.m.ko) (08/06/88)
In article <1988Aug3.160654.9644@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: > >RS232 Usually a synonym for RS232C, the most modern version of RS232. ^^^^^^^^^^^^^ > RS232B and its predecessors are so ancient that they're quite > irrelevant nowadays. > I believe the most modern version is RS232D -tmk