jpd00964@uxa.cso.uiuc.edu (08/23/89)
[null - modem cables] I believe that the following is correct, but I would not testify to it. Computers and terminals are considered terminals in RS-232 terminology while modems are considered computers. I think the terminogy is wrong, but the idea is still there. The thought is that any computer that is hooked up is being used from elsewhere, and therefore not the main concept in RS-232 newspeak. Anyway, if a terminal is hooked to a terminal, then you have data transmit hooked up to data transmit which means no one is receiving. To fix, use a modem with two wires switched and call it a null-modem. Then Each terminal thinks its talking to a computer. Modems are computers so they do not need a null-modem cable. Printers are terminals so they do. Hey, I didn't create this mess, I just confuse it :-> Michael Rutman Softmed
hollombe@ttidca.TTI.COM (The Polymath) (08/26/89)
In article <246300047@uxa.cso.uiuc.edu> jpd00964@uxa.cso.uiuc.edu writes: } }[null - modem cables] } }I believe that the following is correct, but I would not testify to it. } }Computers and terminals are considered terminals in RS-232 terminology while }modems are considered computers. Modems are pretty consistent about this. They're nearly always DCE (Data Communications Equipment). Personal computers and their serial ports, on the other hand, are more subject to the whims of the manufacturer. My old Osborne 1, for example, needs a null modem to talk to a modem through its serial port. So does my SO's PS/2. This allows them to talk to DTE (Data Terminal Equipment) serial printers _without_ a null modem. (Why this was assumed to be the more common case, I don't know. Both our printers use the Centronics parallel ports). }... To fix, use a }modem with two wires switched and call it a null-modem. ... A null modem is a _cable_ with the data lines crossed, among other things. (A true null modem cable crosses a few other things as well. I've got a complete pin-out, but it's easier to just buy one these days -- about $7 at Radio Shack for a null-modem-in-a-DB25-jacket). -- The Polymath (aka: Jerry Hollombe, hollombe@ttidca.tti.com) Illegitimati Nil Citicorp(+)TTI Carborundum 3100 Ocean Park Blvd. (213) 452-9191, x2483 Santa Monica, CA 90405 {csun|philabs|psivax}!ttidca!hollombe