What Serial Switch Is For
There are few situations where the Serial Switch is required. Those programs that don't use the I/O ToolBox routines, but instead directly address the I/O hardware (contrary to Apple's programming recommendations) may have compatibility problems with these IOP-equipped systems.
Because there's no way to bypass the IOP that controls the SWIM and ADB, applications that address that hardware must be modified to work on the Macintosh IIfx, Quadra 900, or Quadra 950.
Some History
This control panel was originally called the Macintosh IIfx Serial Switch 1.0. It was revised and renamed Serial Switch, to reflect that it can also be used with the Quadra 900 and 950. This newer version of the Serial Switch hasn't been as widely distributed as the previous version because most of the third-party incompatibilities have long since been corrected. But since there are still third parties, most notably MIDI developers, who wish to use their own serial drivers, Apple provides the switch to developers to distribute with their applications should their applications require it.
Which Macintosh Models Can Use It
The Serial Switch control panel is designed for systems that contain intelligent I/O processors (IOPs). Only the Macintosh IIfx, Quadra 900, and Quadra 950 have IOPs on the ports for the floppy disk, ADB, and serial I/O. These ASICs feature a built-in microprocessor, DMA controller, timer, and external Static RAM (SRAM), used to off-load floppy disk, ADB, modem, and printer port interrupts. If you use Serial Switch on a Macintosh that has no IOP, you will see the error message you report.
Using Serial Switch Version 1.1
The current version of Serial Switch is 1.1. After launching it, you will see "ver 1.1a1" in the top right corner of the window.
The control panel has two modes:
- Faster. Use this mode when using the IOP.
- Compatible. Enables developer's code to address the SCC hardware directly, bypassing the IOP.
After changing the mode, restart the system to have it take effect.
Where to Get It
You can get the Serial Switch control panel from:
- The MIDI Manager Tools Disk
- The E.T.O. (Essential Tools and Objects) CD-ROM that is sent to developers on a subscription basis
- Apple Software Licensing
Remember, the Serial Switch is still sometimes referred to as the "Macintosh IIfx Serial Switch"; however, regardless of the name, version 1.1 will work on some Quadras too.