[MODEM]
Most modem-related questions and problems should be directed to the Internet Information Center (IIC), but there are some Macintosh-specific issues that commonly cause problems.

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[SERIAL PORT]

The Serial Port

Macintoshes talk to external modems through the serial port. This port has a circular connector with 8 pins, and is usually labeled with either a modem icon or a printer icon (The "Modem Port" and the "Printer Port"; see photo at right). Setting up an external modem is simple: plug the modem into a serial port, and the phone line into the modem. Most Macintoshes have two serial ports that are identical in every way but one: The serial "printer port" is the only port that LocalTalk can use. If LocalTalk is active, then the printer port is marked as "in use" by the system, regardless of whether or not there is actually anything plugged into it. In most situations (particularly when dealing with a Macintosh on WEB), it is best to plug an external modem in to the "Modem Port" (although it will work just as well if plugged into the "Printer Port").

The serial port can become an issue if there are more serial devices than ports. For example, a Macintosh with two serial ports cannot use a StyleWriter printer, a LocalTalk connection, and an external modem at the same time (each requires a serial port). The cheapest solution in this case is to unplug and replug the devices as they are needed, but a switchbox would minimize wear and tear on the serial connectors. If the user switched to Ethernet, the printer port would not be needed by the network and the two serial ports could be used by the modem and printer. PowerBook 5xx Macintoshes and the PowerBook 150 only have one serial port. In order for the serial port to be used for a printer or modem, the network software must be turned off or set to Ethernet in order to free up the port.

Telecommunications software such as Zterm, SitComm, TinCan, InterSLIP, and ARA require you to select the port to be used by the modem (refer to their documentation for instructions). In most cases the software will tell you if you have selected a port that is "in use", but you may get a crash or freeze if the Macintosh gets confused as to which ports are in use by what application (or network). Always check the physical connection and software settings when a problem with the serial port is suspected.

The Communications Toolbox

The Macintosh Communications Toolbox is system software that provides Macintosh applications with standard access to communications services, including data connection, terminal emulation, and file transfer protocols. Communication tools such as an XMODEM file transfer tool or a modem connection tool are available (from Apple or third-party developers) to perform all functions associated with a given communications service. For example, the commercial telecommunications application, "SitComm" (by Alladin Systems) depends entirely on the Communications Toolbox for its functionality. The package comes with several proprietary communication tools that the application uses to telecommunicate. The tools can be used by other Communication Toolbox-aware applications as well

The Communications Toolbox is built into the MacOS versions 7.0 and above. It can be installed in System 6.0 by using the Installer and Communications Toolbox installation script found on ASHD1

(ASHD1/Apple software/Communications 1)

Even though the Toolbox is part of the system software (or after it has been installed into System 6.0), the standard installation does not add any communication tools to the Extensions Folder (within the System folder). In order for the system to support a given tool, it must be copied into the Extensions folder and the computer restarted. Apple's "Basic Connectivity Set" contains the folowing tools, and can be found in the same directory as the Installer on ASHD1:
Connection toolsTerminal toolsFile Transfer tools
Serial ToolTTYText
Modem ToolVT-102XMODEM
AppleTalk ADSP Tool

PowerBook Internal Modems

Many PowerBooks contain internal modems that connect to the computer via an internal modem slot. Although these modem don't plug into the serial port, they still use the serial port circuitry of the Modem port (or the Printer/Modem port in the PowerBook 5xx series and PowerBook150). As far as the MacOS is concerned, there is a device plugged into the serial port. When an application initializes the internal modem, the modem takes control over the serial port. If the port is already in use (by a printer or a network), the Mac will report an error.

Telecommunications software written after the introduction of the Communications Toolbox can usually use the internal modem without problems (assuming they have been configured correctly). But older software that expects every mac to have two serial ports and an external modem may have problems. To deal with possible incompatibility and to allow the use of either the internal modem or the external modem port, use the PowerBook Setup control panel to configure how the internal modem interacts with the serial port.

On PowerBook 1xx-series Macintoshes, the PowerBook Setup control panel lets you select between "Internal Modem" and "External Modem":

[PowerBook Setup Control Panel]
If you select internal modem, the Mac ignores any device plugged into the serial port, and treats the internal modem as if it were plugged into it. If you select external modem, the internal modem is ignored.
On PowerBook 5xx-series Macintoshes, the PowerBook Setup control panel had its controls renamed to say "Normal" and "Compatible". Select Normal to use the internal modem, and Compatible to use the serial port.

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