jhc@mtune.ATT.COM.UUCP (02/05/87)
>In article <8702010550.AA07252@ucbvax.Berkeley.EDU>, rdsnyder@MIT-CCC.UUCP writes: > The person proposed to use modular telephone connectors for connecting > RS-232 serial lines. and that is how they should be used lest some bozo > should happen to plug an RS-232 cable into a telephone jack It is for this exact reason that AT&T's Premises Distribution System utilises a resistor-capacitor pair, inside the little module which also converts from a 4-pair modular jack to a DB-25. They call this beast a 'Terminal Protector'! That way if a terminal gets plugged in to an analog line which is ringing, the cheap little module gets fried and not the expensive terminal. Mind you, the terminal protectors aren't exactly cheap... Modular connectors do have significant advantages over conventional RS-232 DB-25 connectors, especially the brain-damaged ones on the IBM PC and clones. -- Jonathan Clark [NAC,attmail]!mtune!jhc My walk has become rather more silly lately. --- Jonathan Clark [NAC,attmail]!mtune!jhc My walk has become rather more silly lately.
mark@cbosgd.MIS.OH.ATT.COM@rutgers.UUCP (02/13/87)
The typical modular RS232 plug (and everybody and his dog is already using them - all with different pin arrangements) is an RJ-45 (8 wire) connector. Since these are wider than a typical RJ-11 jack, there is little danger of plugging them into the wall. Anybody who makes a true RJ-11 RS232 cable only has 4 wires to work with. After SD, RD, and SG, you've only got one left for CD or DTR or DSR or FG or whatever else you want to carry. Possible, but I sure wouldn't put that in a product I was designing. The modular jacks are becoming very popular for lots of things, because their physical design is very convenient. For example, Starlan uses a modular plug. So does ISDN. If you've ever fought with an Ethernet connector (and tried to keep it from falling off) or hassled with screwing down RS232 (and not bothered) you'll appreciate why the modular jack is so popular. There is concern about people plugging them into the wrong place among some of the product designers. For example, the Starlan connector is an 8 wire RJ-45 type plug, but Starlan itself only uses 4 wires. They deliberately avoided the 2 center wires that are used for the phone line, but instead stuck to some near the outside. This has the unfortunate side effect that you can't go to your favorite grocery store and buy Starlan cable, but it's the price of safety. Mark