Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: nyu notesfiles V1.1 4/1/84; site ur-univax.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!decvax!genrad!panda!talcott!harvard!seismo!rochester!ur-univax!ning From: ning@ur-univax.UUCP Newsgroups: net.micro.mac Subject: Re: Mac-tty pinouts? Message-ID: <16500011@ur-univax.UUCP> Date: Tue, 5-Mar-85 16:13:00 EST Article-I.D.: ur-univa.16500011 Posted: Tue Mar 5 16:13:00 1985 Date-Received: Sat, 9-Mar-85 11:40:51 EST References: <2362@nsc.UUCP> Organization: University of Rochester: Computing Center Lines: 55 Nf-ID: #R:nsc:-236200:ur-univax:16500011:000:2159 Nf-From: ur-univax!ning Mar 5 16:13:00 1985 > The following four connections will make your Mac RS-422 connector into a > standard RS-232 connector. Building a cable with a female 9-pin D connector > on one end and a female (or male, depends upon your modem) 25-pin D connector > on the other is the easiest way to do this. > RS-422 RS-232 > (Mac 9-pin) (Modem 25-pin) > 3 7 > 5 2 > 7 20 > 9 3 I have just finish building an RS-232 cable for my Mac/modem, and it works beautifully. But I didn't use the diagram above, and unfortunately, the diagram above doesn't work with software that looks for the RS-232 signal called DCD (Carrier Detect). The problem is the way it uses the pin 7-to-20 connection. Pin #7 on the Mac is a "listen" line called HSC (High-Speed Carrier?) in RS-422 lingo. Pin #20 on a DB-25 is a "talk" line called DTR (Data Terminal Ready) in RS-232 lingo. The problem is that a modem doesn't send a DTR signal. (It sends a DSR (Data Set Ready) on pin #6, but this is irrelevant, because the Mac is looking for a "Carrier Detect.") The right connection for a DCD is pin #8 on a DB-25. Now that the two "carrier detects" are hooked up, this is what happens. The Mac tells the modem to dial, and when the modem gets the carrier from a remote modem, it makes true the DCD line. When the Mac "hears" a true from its HSC line, then it knows that a distant modem has been hooked-up. Of course, software that ignores the DCD will work, but it might get you sometime in the future. I used the diagram found in the "Open Window" section in March's issue of MacWorld. The article there shows how to hook a Mac up with a Volksmodem. So, I simply matched the signal *names* from the Volksmodem with a D-25 connector. This was my end result: Macintosh Modem RS-232 Signal Name (9-pin DTE) (25-pin DCE) Pin # 3 <---> 7 Signal Ground (GND) 5 ----> 2 Transmit Data (TxD) 9 <---- 3 Receive Data (RxD) 7 <---- 8 Data Carrier Detect (DCD) Note that a cable built this way will also work for a simple RS-232 line to a mainframe. John Lam______________________________________ {allegra,seismo,inhp4}!rochester!ur-univax!jnl PS. No flame intended. (:-)