Newsgroups: comp.sys.apple2.comm Path: news.weeg.uiowa.edu!news.uiowa.edu!uunet!wupost!waikato!comp.vuw.ac.nz!actrix.gen.nz!dempson From: dempson@swell.actrix.gen.nz (David Empson) Subject: Re: Why GS/Mac Hardware Handshake Cable? Organization: Actrix Information Exchange Date: Wed, 11 Aug 1993 12:01:46 GMT Message-ID: <1993Aug11.120146.19086@actrix.gen.nz> References: <2478d6$36e@agate.berkeley.edu> <1993Aug10.110319.1@csusb> Sender: dempson@actrix.gen.nz (David Empson) Lines: 58 In article <1993Aug10.110319.1@csusb> dbrown@csusb (Dan Brown) writes: > In article <2478d6$36e@agate.berkeley.edu>, erichsu@lhasa.berkeley.edu (Eric 2 Hsu) writes: > > Since this hasn't made the FAQ yet, I'll ask anyway. Why is a special GS > > hardware handshaking cable necessary at all? Is it only because Apple left > > off the RTS/CTS signals off its Mini-DIN-8 serial ports? > > No, RTS & CTS are on the GS port, but they're usually not wired on a > basic modem cable. I don't know why, but that's the way someone began to wire > them. The Hardware Handshaking cable simply connects the lines that should > have been connected all along. No they aren't. The IIgs and Mac serial ports have the following pins (in no particular order): TxD-, TxD+ (balanced RS-422 or RS-423 transmit data) RxD-, RxD+ (balanced RS-422 or RS-423 receive data) Handshake Out (from DTR pin of serial chip) Handshake In (to CTS and clock input pin of serial chip) General Purpose Input (to DCD pin of serial chip) Ground The Macintosh is missing the General Purpose Input (at least, the early models are - I don't know if it was added after the Mac II or SE). The RTS pin of the serial chip is used to enable the transmitters (for use with AppleTalk). It has no DSR pin. A standard serial cable connects the "Handshake Out" line to the modem's DTR pin, and the "Handshake In" line to the DSR pin. Apple make a small Mini-Din-8 to DB-25 adapator, which does the above mappings. It also connects the modem's CTS signal to its RTS signal, and feeds this into the "General Purpose Input" line of the IIgs. If you have "DCD Handshaking" enabled in the control panel, it is expecting to use a cable like this - with the modem's CTS signal being fed into the carrier detect input of the serial chip. DTR/DSR handshaking assumes that the "Handshake Out" and "Handshake In" lines are connected to DTR/DSR. This is normally used with a printer, not a modem. With a high-speed modem, you need the modem's RTS/CTS signals to control flow of data, and it is also useful to have the DCD signal to detect carrier. A "handshaking" cable will therefore connect the modem's RTS signal to the IIgs "Handshake Out" line, CTS to the "Handshake In" line, and DCD to the "General Purpose Input" line. I don't know what they do with DSR and DTR on the modem - probably wire them into each other, or leave them disconnected. -- David Empson dempson@swell.actrix.gen.nz Snail mail: P.O. Box 27-103, Wellington, New Zealand Newsgroups: comp.sys.apple2.comm Path: news.weeg.uiowa.edu!news.uiowa.edu!hobbes.physics.uiowa.edu!math.ohio-state.edu!sdd.hp.com!crash!mdavis From: mdavis@crash.cts.com (Morgan Davis) Subject: Re: Why GS/Mac Hardware Handshake Cable? Organization: CTS Network Services (crash, ctsnet), El Cajon, CA Date: 11 Aug 93 20:40:39 GMT Message-ID: References: <2478d6$36e@agate.berkeley.edu> <1993Aug10.110319.1@csusb> <1993Aug11.120146.19086@actrix.gen.nz> Lines: 47 In <1993Aug11.120146.19086@actrix.gen.nz> dempson@swell.actrix.gen.nz (David Empson) writes: >The Macintosh is missing the General Purpose Input (at least, the >early models are - I don't know if it was added after the Mac II or >SE). The SE and Mac II both include GPi support. Must have been the Mac Plus and earlier models that lack it. >A standard serial cable connects the "Handshake Out" line to the >modem's DTR pin, and the "Handshake In" line to the DSR pin. >Apple makes a small Mini-Din-8 to DB-25 adapator, which does the above >mappings. It also connects the modem's CTS signal to its RTS signal, >and feeds this into the "General Purpose Input" line of the IIgs. It should be noted that you do NOT want to use this on your IIGS if you're attaching a modem to it. There is a better scheme. >DTR/DSR handshaking assumes that the "Handshake Out" and "Handshake >In" lines are connected to DTR/DSR. This is normally used with a >printer, not a modem. However, to avoid any confusion that statement may cause, if you have a properly wired hardware handshaking modem cable, you want to set the DTR/DSR Handshaking option to Yes. Apple really should have named this something like "Input/Output Handshaking" and DCD Handshaking to "Input Handshaking". >I don't know what they do with DSR and DTR on the modem - probably wire >them into each other, or leave them disconnected. Disconnected. The modem's DSR is not usually used at all. Apple's suggestion for a high-speed, hardware handshaking modem cable involves tying the HSKo->RTS connection to the modem's DTR signal in a Y configuration. This would allow you, through modem settings, to utilize HSKo for either hardware flow control or as support of the DTR signal, which is normally used to tell a modem to disconnect. With this cable, you can have either option, but only one at a time. That is, you can't have hardware flow control and DTR to disconnect at the same time, unfortunately. While they're nice and compact, the DIN-8 serial ports are one pin short for providing decent modem control. Apple should have stayed with the DB-9 port, still encouraging the RS-422 wiring scheme for improved reliability and performance.