Newsgroups: comp.sys.apple2.comm Path: blue.weeg.uiowa.edu!news.uiowa.edu!hobbes.physics.uiowa.edu!math.ohio-state.edu!howland.reston.ans.net!wupost!waikato!comp.vuw.ac.nz!actrix.gen.nz!dempson From: dempson@actrix.gen.nz (David Empson) Subject: Re: Apple IIgs modem port Message-ID: Organization: Actrix Information Exchange References: Date: Thu, 28 Jul 1994 08:26:43 GMT Lines: 91 In article , Jim Kyriannis wrote: > > According to the Apple IIgs Hardware Reference, it looks like the IIgs modem > port supports a wierdish sort of hardware hadshaking, using the DTR instead of > an RTS. Does anyone know if this is the same behavior as the Mac Quadras? The IIgs and all Macs only have one outgoing flow control line, officially called "Handshake Out". The IIgs firmware usually refers to it as "DTR" and this is certainly its most common use (going to pin 20 of a DB-25 to plug into a modem). The main incoming flow control line "Handshake In" is usually used as DSR (going to pin 6 of a DB-25). The IIgs and all Macs since the SE have supported the "General Purpose Input", which is called DCD by the IIgs firmware. [Incidentally, the so-called DTR and DSR signals actually come from the RTS and CTS pins of the Z8530 SCC. The chip doesn't have DSR and DTR pins.] See below for an essay on IIgs handshaking methods. In your case, you need a "hardware handshaking" cable, which routes the "handshake in" and "handshake out" lines to the RTS and CTS pins of the modem. You cannot control the modem's DTR line at the same time, so you should tell the modem to ignore DTR (AT&D0). The DCD input of the IIgs can be connected to the modem's DSR or DCD line, depending on what your software's driver expects (probably DCD). I can't give you pin numbers right now, but here are the names and connections: IIgs Modem Hshk Out 4 RTS Hshk In 5 CTS TxD- 2 TxD Gnd 7 Gnd RxD- 3 RxD TxD+ No connection GPI (DCD) 8 DCD or 6 DSR, but not both RxD+ Must be connected to ground (pin 7) You could connect the handshake out line to DTR (pin 20) as well as RTS, which would allow you to use the outgoing flow control line to serve as either RTS or DTR, depending on how you've configured the modem. You'd have to be careful about setting the AT&D and AT\Q commands. You'll have to tell your comms software to use hardware handshaking, or use an appropriate driver. If you're writing your own programs and are relying mainly on the firmware, just make sure "DSR/DTR Handshaking" is enabled in the control panel. [Notes on IIgs flow control methods follow] The IIgs control panel provides a flow control scheme it calls "DSR/DTR handshake", which basically means to use the "Handshake Out" and "Handshake In" signals to control flow of data in the manner of CTS/RTS with a high-speed modem, or the DTR signal from a serial printer. It also supports something called "DCD handshaking", which uses the General Purpose Input (DCD) to prevent transmission. This doesn't make much sense, until you encounter the standard Mini-Din-8 to DB-25 cable adaptor that Apple used to supply (I bought two shortly after I got my IIgs in 1987). These cables are wired as follows (I'm not sure if I have the pins in the right order - no manuals on hand). IIgs DB-25 female (wired as a DCE) Hshk Out 6 (DSR) Hshk In 20 (DTR) TxD- 3 (RxD, from a printer/terminal point of view) Gnd 7 (Gnd) RxD- 2 (TxD, from a printer/terminal point of view) TxD+ No connection GPI (DCD) 4 (RTS) and 5 (CTS) RxD+ 7 (Gnd - used to bias the receiver into RS-423 mode) Note that the "DCD" pin of the IIgs goes to CTS and RTS, which are tied together. If this cable was used with a device that asserted RTS, then the device would get its own RTS signal back as CTS, and taking RTS away would prevent the IIgs from transmitting if "DCD Handshake" is turned on in the control panel. -- David Empson dempson@actrix.gen.nz Snail mail: P.O. Box 27-103, Wellington, New Zealand Path: news1.icaen!news.uiowa.edu!uunet!in4.uu.net!nntp.giganews.com!worldfeed.gte.net!intgwlon.nntp.telstra.net!news.telstra.net.nz!news.wlg.netlink.net.nz!news.actrix.gen.nz!dempson From: dempson@actrix.gen.nz (David Empson) Newsgroups: comp.sys.apple2 Subject: Re: Need Point-to-Point Patch for 14000 BAUD rate Date: Sun, 26 Jul 1998 16:01:56 +1200 Organization: Empsoft Lines: 105 Message-ID: <1dcs6jl.6wl5f24jy960N@dempson.actrix.gen.nz> References: <6pcr5h$1gs6$1@lynx.unm.edu> NNTP-Posting-Host: news2.actrix.gen.nz X-Newsreader: MacSOUP 2.3 Xref: news1.icaen comp.sys.apple2:137270 stephen e buggie wrote: > I use POINT-TO-POINT modem software. I've now got a Promodem 144e modem > by Prometheus. Its an external modem connected to the modem serial port > of the Rom 3 IIgs. > > The problem is that the two fastest speeds on Point-to-Point are: > > 9600 BAUD and 19200 BAUD. > > The modem goes 14400 baud at its fastest rate. You need to distinguish between two speeds here: - The speed at which the modem transfers data over the telephone line (the carrier speed, if you like). - The speed at which the modem and computer exchange data. These two are not necessarily the same for any modem faster than 2400 bps (and even for some 2400 bps modems). If the modem supports error correction and/or data compression, then the computer-to-modem speed must be HIGHER than the modem's carrier speed. If the modem does not support error correction or data compression, and either the modem or computer has no support for handshaking, then the modem's carrier speed will match the speed at which the computer is connected to the modem. (This applies to all 300 bps modems, all 1200 bps modems that I know of, and most 2400 bps modems.) In the case of a 14k4 modem, you would normally be using error correction and data compression (either MNP-4 and MNP-5, or V.42 and V.42bis), so the computer should be set to talk to the modem at a speed higher than 14400 bps. I have found that 19200 is sufficient. (It is not optimal if you are sending or receiving uncompressed text data, for example, but it is good enough for most situations.) The main catch: handshaking is required between the computer and modem, so that the modem can tell the computer to stop sending data if it cannot keep up (depending on error recovery, how compressable the data is, etc.) The best option is to use hardware handshaking. This raises the question: does Point-to-Point support hardware handshaking? I don't know the answer to this. If it obeys the IIgs Control Panel settings, then all you should need to do is enable DTR/DSR handshaking in the IIgs control panel, and ensure that your modem cable connects to the modem as follows: The pins on the IIgs connector are numbered as follows (looking at the back of the computer; swap these horizontally if you are looking at the pins on the cable): 8 7 6 5 4 3 2 1 The cable pinout should be: IIgs Modem (DB-25) 1 4 Handshake, computer to modem 2 5 Handshake, modem to computer 3 2 Data, computer to modem 4 7 Signal ground 5 3 Data, modem to computer 6 (no connection) 7 8 Carrier detect, modem to computer 8 (must be connected to IIgs pin 4 or modem pin 7) This is a standard "hardware handshake" cable for the IIgs (or Mac). The traditional modem cable connects the flow control signals (pins 1 and 2) to the DSR and DTR pins on the modem, which are not used for handshaking. If you are using an existing cable that was previously used with a slower modem, you will probably need to get it modified, or buy a new cable. In the meantime, your existing cable will only work reliably if you disable hardware handshake, error correction and data compression capabilities in the modem, and select 9600 bps on the computer. > BTW, I have a second identical ProModem 144e that does not work. The CD > (carrier detect) lamp is always on. I looked inside the modem case and > there are no obviously burned components. Any suggestions???? This might be a setting: the AT&C command is used with most modems to specify whether the Carrier Detect signal is to be used. AT&C0 forces it to be permanently active, AT&C1 allows it to follow the real carrier detect state. If using AT&C1 does fix it, use AT&W to write the updated setting into the modem's nonvolatile memory. Ideally, you should do an AT&F to restore factory default settings, then go through the manual and identify which settings you wish to change, then write the settings using AT&W. A subsequent power-on or reset command (ATZ) will restore the saved settings. -- David Empson dempson@actrix.gen.nz Snail mail: P.O. Box 27-103, Wellington, New Zealand