Path: utzoo!attcan!uunet!munnari.oz.au!uhccux!ames!sgi!rpw3@rigden.wpd.sgi.com From: rpw3@rigden.wpd.sgi.com (Rob Warnock) Newsgroups: comp.dcom.modems Subject: 134.5 baud == IBM 2741 (was: Re: Why 300 baud?) Message-ID: <61463@sgi.sgi.com> Date: 2 Jun 90 04:54:30 GMT References: <9686@discus.technion.ac.il> <1990May31.025608.18545@Neon.Stanford.EDU> Sender: rpw3@rigden.wpd.sgi.com Reply-To: rpw3@sgi.com (Rob Warnock) Organization: Silicon Graphics, Inc., Mountain View, CA Lines: 68 In article kindred@telesci.uucp writes: +--------------- | Along the lines a strange baud rates, I personally have run | into the all time favorite baud rates of 134.5 and 1050. The 134.5 | was used in a six bit commodities ticker... +--------------- Oh, 134.5 baud was used in stuff *far* more important than a commodities ticker -- that was the speed of the venerable (or damnable) IBM 2741 "Selectric I/O Writer". That is, a Selectric typewriter fixed up with a bit-serial interface. The 2741 was *the* hard-copy remote terminal in much (most? all?) of the IBM world for a number of years, not to mention a few folk who insisted on using it on TOPS-10 and Unix systems because the print quality was far better than any ASR-3x. (Well, it *was* better.) Of course, the 2741 wasn't all that easy to deal with: - It was truly half-duplex. - The keyboard locked when you hit , and didn't unlock until an unlock signal came out from the host. - The host couldn't send to you if the keyboard was locked. - *Some* (but not all) 2741's had an extra-cost option to allow the host to lock a keyboard even if you were typing, by sending a . There was another option that let you lock the keyboard and tell the host about it without typing . And another that let you send an to the host even while it was typing. - And of course, the character set wasn't within *miles* of ASCII, and wasn't even EBCDIC, but something all its own. (For example, the 2741 sent the bits in a byte backwards from TTYs.) - Like the TTY Model 29, it had "stateful" shifts. You sent a shift code and then you were stuck until you unshifted. (Or sent a ?) - And of course, if you got a line error at exactly the wrong time, you could get stuck in a state you couldn't get out of. (At least, not easily. And not at all if you were an ordinary user without knowledge of the magic incantations to tease it out of its tiff.) I had the dubious honor of being one of the folk at Digital Communications Associates (circa 1977?) who helped to make a 2741 -- when connected through a DCA "SmartMux" -- be able to emulate an ASCII terminal to a DEC PDP-10... all the way up to and including being able to type ASCII control characters (you *do* want to be able to ^C your job, don't you?) and do (sort of) character-at-a-time I/O. That's right, we used all three "options" mentioned above plus a bunch of special code in the SmartMuxes and in a custom TTY driver for the PDP-10 to allow such abominations as editing with TECO ("sABCDEF0tt" is the same as ed's "s/ABC/DEF/p") and debugging with DDT ("123/" caused location "123" to get typed out -- note there's no ). Two notable installations were at the Wharton School of Business in Pennsylvania, and at Western Electric in New Jersey. (Many hours in the middle of several nights before we finally figured out how/why an unexpected "unlock" to the terminal could sometimes crash the PDP-10.) We later did a subset of the reverse, that is, making an ASCII terminal look to an IBM host as if it were a 2741. By the way, that commodities ticker you spoke of almost certainly was emulating a 2741. Nothing else I know of went at that speed. -Rob ----- Rob Warnock, MS-9U/510 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311