CHAPTER 2
Architecture
The internal modem is a separate module that contains the data pump IC and the interface to the telephone line (DAA). For more information about the modem, see “Internal Modem” (page 30).
Sound Circuitry
The sound circuitry, called Snapper, is connected to the Intrepid IC by a standard IIS (inter-IC sound) bus. The Intrepid IC provides DB-DMA (descriptor-based direct memory access) support for the IIS port.
Note: In the device tree, the sound circuitry is named “sound”.
The Snapper circuitry includes a signal processing IC that handles the equalization and volume control functions, a codec IC that performs A-to-D and D-to-A conversion, and a power amplifier that drives the headphone jack.
All audio is handled digitally inside the computer. The Snapper circuitry performs digital-to-analog conversion for the audio signals to the internal speakers and the headphone jack.
For a description of the features of the sound system, see “Sound System” (page 49).
Power Controller
The PowerBook G4 17-inch computer can operate from a 15 volt power outlet on an airline, but for safety reasons, the computer will not allow battery charging. In order for the computer to detect the connection to airline power, the airline power cable should have a sense resistor of 24.3 K ohms +/-1% connected between the power plug's shell and ground.
The PowerBook G4 17-inch computer has a variable speed fan control circuit and a thermal circuit that will force the unit into reduce-processor mode at 72 degrees Celsius and into sleep mode if the processor temperature exceeds 79 degrees Celsius.
The power management controller in the PowerBook G4 17-inch computer is a custom IC called the PMU99. It supports several power-saving modes of operation, including idle, doze, and sleep.
Note: In the device tree, the power controller is named “via-pmu”.
A device’s ID voltage limits determines how the PMU identifies the power adapter. The PowerBook G4 17-inch computer is designed to use the 65-Watt Apple Portable Power Adapter which ships with it. Although you can use a 45-Watt Apple portable power adapter with a 17-inch PowerBook G4 computer, it may not provide sufficient power during some activities and power may be drawn temporarily from the battery. Should the battery become discharged, you may need to plug in the 65-Watt Apple Portable Power Adapter that came with the computer in order to start it up.
AirPort Extreme Interface
AirPort Extreme contains a media access controller (MAC), a digital signal processor (DSP), and a radio-frequency (RF) section.
