Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!usc!apple!well!tswift From: tswift@well.sf.ca.us (Theodore John Swift) Newsgroups: comp.sys.tandy Subject: Re: Need help connecting Tandy 200 to Mac 512K Message-ID: <23620@well.sf.ca.us> Date: 14 Mar 91 22:07:57 GMT References: <1991Mar5.134533.3044@waikato.ac.nz> <1991Mar5.134902.3046@waikato.ac.nz> Organization: Whole Earth 'Lectronic Link, Sausalito, CA Lines: 47 furmanm@hotcity.uucp (Michael Furman) writes: > What you need to do on the Mac, is turn the "handshake" off. Actually, for RS-232 work, you can just ignore them, since they're only used (or necessary) for high-speed clocked stuff. The following information is from _Inside Macintosh Vol. 4_, p. 248. > It looks as if > the Mac outputs are "current loop", and that gets a little bit complicated. > The Tandy side is no problem, since it is standard RS-232. I don't know that > much about the Mac, so, if anyone else can, add to this. You might also want > to go to a Mac.hardware newsgroup and ask them. The Mac's serial ports are RS-422 (or 423, according to _IM4_), not to be confused with the old (generally 20 milliamp) current loop. RS-422 uses a differential pair (TX+, TX-; RX+, RX-) to transmit data: when TX+ is "high", TX- is "low", and vice-versa. "high" is +5V and "low" is -5V, I think. RS-232 generally likes about +-12V, but will work with much less. To "fake" RS-232 on the Mac, connect TX+, RX+, and Ground to the appropriate lines on your RS-232 side. Here's the pinout as listed in _IM4_; It basically agrees with Michael's, with the exception of pins 3, 5, and 7. Pin Function my comments ------- ---------------------- ----------- 1 Handshake out 2 Handshake in or external clock 3 Transmit data minus not ground 4 Signal ground 5 Recieve data minus not ground 6 Transmit data plus 7 Not Connected according to _IM4_ 8 Recieve data plus As Michael recommends, it's good to have a breakout box to troubleshoot, but if one is not available, a bit of experimentation with these lines should do the trick. Just about any terminal emulator on the Mac should work. Good luck. -Ted -- ---------------------- Ted Swift tswift@well.sf.ca.us "You bally well are informed, Jeeves! Do you know everything?" "I don't know, sir" ~P.G. Wodehouse