C H A P T E R 3
Devices and Ports
■Interrupt transfers, used for human interface device (HID) class devices such as keyboards and mice, as well as devices that report status changes, such as serial or parallel adaptors and modems.
■Isochronous transfers, used for
Version 1.0 of the Macintosh USB system software provides functions that support only control, bulk, and interrupt transfer types.
USB Compatibility Issues
The USB ports take the place of the ADB and serial I/O ports found on earlier Macintosh computers, but they do not function the same way. The following sections describe the differences.
ADB Compatibility
Apple is providing an ADB/USB shim to support processes that control ADB devices by making calls to the ADB Manager and the Cursor Device Manager. The ADB/USB shim makes it possible for processes that support an ADB keyboard to work with the USB keyboard equivalent.
For example, the ADB/USB shim allows applications to set the caps lock and num lock LEDs on the Apple USB keyboard. The ADB/USB shim also allows the Cursor Device Manager to support a USB mouse.
Keyboards other than the Apple USB keyboard can be used with the iMac computer, but they will be treated as having an ADB device ID of 2.
IMPORTANT
The ADB/USB shim does not support other types of ADB devices. ▲
Note
The ADB/USB shim is built into the Mac OS ROM image on the iMac computer and will be included in the Mac OS ROM image on future Power Macintosh systems that have USB ports. For more information about the Mac OS ROM image, refer to Chapter 5, “Software.” ◆
30USB Ports
