regoli@silver.bacs.indiana.edu (michael regoli) (07/18/88)
]:[ before i go crazy trying to do something that can't be done, does anyone know a safe limit on the length of a serial cable? i'd like to run a serial cable approximately 30 feet @ 9600 bps to drive a laser.
hedrick@athos.rutgers.edu (Charles Hedrick) (07/19/88)
If by serial you mean RS232 async, there are official limits on distance. They depend upon speed. I.e. you can get farther at slower speeds. At 9600 I think the official limit is something like 50 feet. It goes up to several hundred feet at 300. But these limits are incredibly conservative. (That's why I'm not taking the trouble to look up the actual numbers.) Lots of people use 9600 on cables that are several hundred feet long. We do at Rutgers. There is generally no problem. It depends upon keeping it away from big motors and other things that generate noise, on having solid grounding, etc. Most people seem to consider RS232 at 9600 as being OK for just about anything inside a single building. I'm sure somebody from the Pentagon is going to tell me that they have to use microwave with 2 repeaters to get from one end of their building to the other, but for buildings of the size used in universities, things work. You should not use RS232 -- or any other wire -- between buildings, because lightning will tend to fry the equipment that is connected to it. Also, slight differences in ground may cause surprising large currents to flow in the cable. You want to use fiber between buildings.
hollen@spot.megatek.uucp (Dion Hollenbeck) (07/19/88)
From article <1986@silver.bacs.indiana.edu>, by regoli@silver.bacs.indiana.edu (michael regoli): > > before i go crazy trying to do something that can't be done, does > anyone know a safe limit on the length of a serial cable? i'd like > to run a serial cable approximately 30 feet @ 9600 bps to drive a > laser. I believe that RS232 is spec'ed at 9600 baud for about 100 feet, however, here at work, we commonly run 9600 baud at 1000 feet plus to our terminals all over the building with no problem at all. Dion Hollenbeck (619) 455-5590 x2814 Megatek Corporation, 9645 Scranton Road, San Diego, CA 92121 seismo!s3sun!megatek!hollen ames!scubed/
bear@bgsuvax.UUCP (Michael D. Bear) (07/19/88)
I have worked with/installed many serial cables that are longer than you want to install, with no problems. I think the RS232 definition allows a maximum length of 50', but I have seen cables several hundered feet long that worked with no problem. The only thing I might reccommend is that if it *is* longer than 50', you may want to use shielded cable. -- Michael D. Bear UUCP .!cbosgd!osu-cis!bgsuvax!bear Computer Technician CSNET bear@bgsu.edu Bowling Green State University ARPANET bear%bgsu.edu@relay.cs.net (419) 372-2104
brb@akgua.ATT.COM (Brian R. Bainter) (07/19/88)
From article <1986@silver.bacs.indiana.edu>, by regoli@silver.bacs.indiana.edu (michael regoli): > > ]:[ > > before i go crazy trying to do something that can't be done, does > anyone know a safe limit on the length of a serial cable? i'd like > to run a serial cable approximately 30 feet @ 9600 bps to drive a > laser. I could be hopelesly wrong, but I think that RS232 "specs" say that it is good for 100 feet. I don't know if this is correct, but I have had fairly good success at about 300, but there again, 300 feet may be the "spec" instead of 100. In other words, 30 feet should be no problem. -- Brian R. Bainter AT&T Technologies Atlanta Works {cbosgd, gatech, ihnp4, moss, mtune, ulysses}akgua!brb
tomk@lakesys.UUCP (Tom Kopp) (07/19/88)
In article <1986@silver.bacs.indiana.edu>, regoli@silver.bacs.indiana.edu (michael regoli) writes: # before i go crazy trying to do something that can't be done, does # anyone know a safe limit on the length of a serial cable? i'd like # to run a serial cable approximately 30 feet @ 9600 bps to drive a # laser. You should have no problem. I've heard that as a rule, you don't need a modem or a power booster for serial connecting computer until after you cross 50'. Where I go to school, we've got things hooked up to a couple of hundred feet apart w/ no trouble. -- _____ _____ |"Reading computer manuals without |tomk@lakesys.UUCP | | | the hardware is as frustrating as |uunet!marque!lakesys!tomk | \_| | reading sex manuals without the |uunet!uwmcsd1!lakesys!tomk ------------- software" - Arthur C. Clarke ----------------------------
dmt@mtunb.ATT.COM (Dave Tutelman) (07/19/88)
I guess I'm getting curmudgeonly in my old age, but there seems a lot of guessing posted on the net in the name of being helpful. (Yes, I do it myself sometimes, when constrained by home/office spacial displacement :-) This discussion got to me because EVERYBODY knows the reference where the answer can be found but NOBODY looks it up, preferring to post admittedly vague recollections. Here's what the standard actually says: RS232 - Speed to 20 kb/s, length to 15 m (50 ft). Section 3.1 says "longer cables are permissible, provided that the resulting load capacitance ... does not exceed 2500 pF." Usually you can get away with it, but it ain't guaranteed. The foreword to RS232-C (1981) points to RS449 for higher speeds. Since 449 can interwork with 232, and since some serial ports have upgraded their drivers, it's worth looking at RS449. RS449 - supports 2 physical interfaces: RS422 for balanced circuits. RS423 for unbalanced circuits. It is possible to interwork RS423 and RS232 interfaces, provided the proper lead transposition. The actual speeds and distances in the spec for unbalanced operation are: Speed to 20 kb/s, length to 60 m (200 ft). However, explanatory note 6.10 says that, with proper wave shaping, you can get to 60 m at a speed of 60 kb/s. RS423 - This standard goes beyond the detail in RS 449, giving curves of distance vs. speed for various wave shaping. This is probably more than you really wanted to know, and in some sense less; you wanted to know about YOUR serial interface. Here's how: - Look at the driver and terminator chips on the leads. Get the part numbers, and look them up in the catalog. - If the catalog says they are compatible with RS449 or RS 423, you can get 200 feet safely. If not, you can get 50 feet safely. - In either event, you can exceed these distances if you use low-capacitance cable and connectors, or are generally not too unlucky in your environment. - If you try the above, and get flaky operation, well the standard didn't guarantee it. HOWEVER, lower speed and longer distance sometimes work. (See RS423 if you want the exact details.) +---------------------------------------------------------------+ | Dave Tutelman | | Physical - AT&T - Lincroft, NJ | | Logical - ...ihnp4!mtuxo!mtunb!dmt | | Audible - (201) 576 2442 | +---------------------------------------------------------------+
haugj@pigs.UUCP (Joe Bob Willie) (07/20/88)
In article <1986@silver.bacs.indiana.edu> regoli@silver.bacs.indiana.edu (michael regoli) writes: >before i go crazy trying to do something that can't be done, does >anyone know a safe limit on the length of a serial cable? i'd like >to run a serial cable approximately 30 feet @ 9600 bps to drive a >laser. rs-232 cables can be run up to 150 feet without difficulty, even longer lenghts with higher quality cables and connectors. the most important things is to use a shielded cable and connector hoods. after making up the regular connections, such as pins 2, 3, and 7, connect one end of the cable to the ground on pin 1 of a 25 pin connector. the 9 pin connectors only have 1 ground so you will have to make that connection at the laser end. also, avoid routing the cable near ac power lines or florescent lights. those will induce noise onto the serial cable. - john. -- John "Evil USENET User" F. Haugh II HECI Exploration Co, Inc., Dallas UUCP: ...!killer!rpp386!jfh jfh@rpp386.UUCP :DOMAIN **** Trivia question of the day: VYARZERZIMANIMORORSEZASSEZANSERAREORSES? **** "You are in a twisty little maze of UUCP connections, all alike" -- fortune
john@wa3wbu.UUCP (John Gayman) (07/20/88)
In article <2654@bgsuvax.UUCP>, bear@bgsuvax.UUCP (Michael D. Bear) writes: > > worked with no problem. The only thing I might reccommend is that if it *is* > longer than 50', you may want to use shielded cable. I beleive the maximum distance is reduced when using shielded cables. I'm looking at the recent Black Box catalog and all of their distance ratings are reduced substantually if using shielded cable. I beleive this is due to the high capacitance per foot actually attenuating the signals. Anyone have any real specifics along these lines ? I beleive there is a tradeoff as far as using shielded cables to eliminate interferrence and trying to sqeeze the maximum distance out of an interface. John -- John Gayman, WA3WBU | UUCP: uunet!wa3wbu!john 1869 Valley Rd. | ARPA: wa3wbu!john@uunet.UU.NET Marysville, PA 17053 | Packet: WA3WBU @ AK3P
isaac@gethen.UUCP (Isaac Rabinovitch) (07/25/88)
In article <1986@silver.bacs.indiana.edu>, regoli@silver.bacs.indiana.edu (michael regoli) writes: > before i go crazy trying to do something that can't be done, does > anyone know a safe limit on the length of a serial cable? i'd like > to run a serial cable approximately 30 feet @ 9600 bps to drive a > laser. Several others have given good practical answers, but I want to chime in with a more general answer. It's hard to answer questions like this because (a) Not one of the RS232 interfaces completely complies with the standard (usually for good reason); (b) Many RS232 uses are not for the purpose originally intended (connection to a modem at less than 50'); and (c) there are a lot of hardware variations, though PCclones seem to be almost standard these days. At first glance, I would have said, Yes, of course, you're connecting a device less than 50' from the host, even poor hardware should be able to handle it. But does "standard" hardware always go up to 9600 baud? Can't remember. As too often happens in PC Land, a simple, clear, general question has no general answer. I'd give odds of about 100 to 1 that the setup you describe will work, especially if (as others suggested) you use shielded cable -- you should probably use shielded cable anyway. But if there *is* any doubt, I'd use a dumb terminal or terminal emulator to test the interface before doing something more sophisticated. The odds are not nearly as good at longer distances and higher speed. Most hardware makers seem to make RS232 that can easily go several hundred fee and faster than 1 mega-bps -- but which ones? I think the only good general answer is to take it one small step at a time.