Apple Desktop Computer manual USB Controller, Video Display Subsystem, Built-in Modem

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C H A P T E R 2

Architecture

■the built-in modem

■the infrared link

■the Ethernet port

■the sound ASIC

■the internal IDE hard drive

■the internal CD-ROM drive

■the power manager IC

The Paddington IC is similar to the Heathrow IC used in the Power Macintosh G3 computers and Macintosh PowerBook G3 computers. The main difference is that the Paddington IC supports 100Base-TX Ethernet as well as 10Base-T.

USB Controller

The USB controller is a standard IC with two USB connectors. The register set complies with the Open Host Controller Interface (OHCI) speciﬁcation.

Video Display Subsystem

The display subsystem consists of a graphics controller ASIC, 2 MB of SGRAM on the main logic board, and a connector for an additional 2 MB or 4 MB of SGRAM on an SO-DIMM. For information about the SGRAM SO-DIMM, see Chapter 4, “Expansion.”

The graphics controller IC is an ATI Rage IIc. It contains 2D and 3D acceleration engines, a digital video port, front-end and back-end scalers, a CRT controller, and a PCI bus interface with bus master capability.

For information about the display and supported resolutions, see Chapter 3, “Devices and Ports.”

Built-in Modem

The built-in hardware modem is a separate module that is connected to the SCC port A of the Paddington IC. The module contains a modem controller IC, a datapump, and the interface to the telephone line (DAA).

Main Logic Board

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Contents Apple iMac Computer Page Contents RAM Expansion Devices and PortsRtas SoftwareRtas NV-RAM Appendix Abbreviations IndexFigures and Tables Page About This Developer Note Contents of This NoteSupplemental Reference Documents PowerPC G3 MicroprocessorMac OS ATA DevicesOpen Firmware USB DevicesE F a C E Introduction Features Shows a front view of the computer Case and External FeaturesFront view 2Side view showing I/O bay System Software Compatibility IssuesVideo RAM Expansion Modules Main RAM Expansion ModulesUSB Ports and Devices Page Architecture Architecture G3 Microprocessor Processor moduleBackside Cache Memory Controller and PCI Bridge Main Logic BoardController IC Video Display Subsystem USB ControllerBuilt-in Modem Infrared Link Module Devices and Ports USB Ports USB ConnectorsGND Transfer Types SupportedADB Compatibility USB Compatibility IssuesMacintosh-To-Macintosh Connections Serial Port CompatibilityUSB Storage Devices USB ControllerKeyboard Layout KeyboardKeyboard and USB MouseVideo Display Hard Disk DriveSound System Infrared Communication LinkSound Outputs Sound InputsBuilt-in Microphone External Sound InputExternal Sound Output Sound SpeciﬁcationsHeadphone Jacks Total harmonic distortion Internal Modem Ethernet PortPage RAM Expansion Expansion Slots Removing the Logic Board AssemblyPlacing the Computer Face Down Unfastening the Cables Removing the bottom coverRAM Expansion Removing the Retaining Screws 3Logic board assembly handle and retaining screwsRemoving the EMI Shield Removing the Logic Board AssemblyLocations of the Expansion Slots 6Locations of the RAM expansion slots Main RAM ExpansionElectrical Design of RAM SO-DIMMs Mechanical Design of RAM SO-DIMMsSdram Devices Conﬁguration of RAM SO-DIMMs Address Multiplexing RAM SO-DIMM Electrical LimitsVideo RAM Expansion Page Software Why Make This Change? What Has Changed Features of the New Approach RAM Footprint PerformanceUser Experience Data Structures and FilesBoot ROM Contents Rtas Mac OS ndrv DriversToolbox Image File Contents Trampoline Code NewWorld Boot ProcessToolBox ROM Image Interrupt Handling What Is DifferentRAM Footprint Outmoded ResourcesStartup Disk Control Panel NanoKernelInterrupt Layout Open Firmware and the Device TreeMachine Identiﬁcation Software Abbreviations Chrp NMI Page Index Nvram X, Y, Z Allen Watson