chuqui@nsc.UUCP (Chuq Von Rospach) (02/14/85)
Sigh. I've asked this before, and succeeded in misplacing the answers. Can someone drop me a note with the pinouts I need to get a Macintosh to tie into an RS232 line? Thanx, chuq -- From left field, near the warning track: Chuq Von Rospach {cbosgd,fortune,hplabs,ihnp4,seismo}!nsc!chuqui nsc!chuqui@decwrl.ARPA Even though a poem be a thousand words, but made up of senseless words, one word of a poem is better, which if a man hears, he becomes quiet. --The Dhammapada
briand@tekig1.UUCP (Brian Diehm) (02/18/85)
From postnews Mon Feb 18 11:17:37 1985 > Sigh. I've asked this before, and succeeded in misplacing the answers. Can > someone drop me a note with the pinouts I need to get a Macintosh to tie > into an RS232 line? *** REPLACE THIS LINE WITH YOUR MESSAGE *** *** NO! *** 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 Good telecommuning! -Scott Phillips Tektronix, Inc.
ning@ur-univax.UUCP (03/06/85)
> 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. (:-)
jsp@unccvax.UUCP (Joel Patterson) (03/08/85)
Most of the mac<->modem pinouts I have seen on the net have neglected DTR. Some modems require a high signal on pin 20 (DTR) in order to connect, answer the phone, or do anything but sit there. On some this is an option which can be switched off. In any case you must either turn the option off or strap DTR high. Most modems supply a constant high on pin 9 and jumpering it to pin 20 should do the trick. Pin 6 (DSR) may also be an alternate source for this signal. * Strapping DTR high also implies that the modem always thinks the mac is ready and waiting to communicate so it may answer your phone when you least expect it. This can be very annoying to sweethearts, customers, and bosses, since the modem usually answers on the first ring and you don't. So turn the modem off when not actually in use or awaiting calls. happy telecommunicating jsp
ning@ur-univax.UUCP (03/17/85)
In my previous article to this newsgroup, I gave details on how to build a cable between a Mac and a modem. Fortunately, that worked with my modem; unfortunately, it doesn't necessarily work with modems that expect a "Data Terminal Ready" as jsp@unccvax said in his/her reply to my article. Jsp was correct in saying that my cable might not work with modems that expect a DTR. And mine had the option set to ignore the DTR. I didn't realize that the cable wouldn't work until I tried to attach a hard-wired Unix on the other end of the cable. The problem was that the Unix's serial ports expected a DTR and a "Request to Send" from the Mac, and the Mac doesn't send any of these signals. The solution that I found was to trick the Unix by "bouncing" the signals sent by Unix back to itself. Since the serial port on the Unix was wired as "Data Communications Equipment," it sent the signals "Data Set Ready" and "Clear to Send." In RS-232 convention, these signals are analogous to the "Data Terminal Equipment" signals of "Data Terminal Ready" and "Request to Send." The point of this is that I could "trick" the Unix into thinking that my Mac was ready to accept data by sending the DSR back into the DTR, and the CTS back into the RTS. So whenever the Unix was ready to send data, it would find that the Mac was ready to accept; and whenever it was ready to accept data, it would find that the Mac was ready to send. This usually works, but sometimes this faked handshaking might pose a problem. (In my case, both the Mac and Unix were ready to accept data anyway.) But without another kludge, the Mac can't make use of these signals even if the Unix depended upon them: Some mainframes that don't use X-ON and X-OFF (DC1 & DC3 by other names) might use DSR and CTS to tell the Mac that it is not ready to accept data. The kludge is to wire one of these signals (depending on how your mainframe's serial ports toggle these signals) into the Mac's Carrier Detect, and with software the uses the Carrier Detect, you get one-way handshaking. So the forged handshaked, which is what I use for both the hard-wired serial ports and my modem looks like this: 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) +--- 6 Data Set Ready (DSR) +--> 20 Data Terminal Ready (DTR) +--- 5 Clear to Send (CTS) +--> 4 Request to Send (RTS) The one way handshake (which I haven't tried, but in theory should work) is like the forged handshake with this exception: 6 DSR 7 HSC <---< or 5 CTS Now that you see the big mess of RS-232, you can see why people prefer to use X-ON and X-OFF--that is, until they have to enable and disable it in order to use XMODEM with macput and macget. -- Happy happy Telecommunicating, John Lam_____________________ {allegra,seismo,inhp4}!rochester!ur-univax