Block Diagram

Figure 2-1 is a simplified block diagram of the main logic board. The diagram shows the input and output connectors, the Intrepid 2 IC, and the major buses.

Main IC and Buses

The architecture of the 15-inch PowerBook G4 is designed around the PowerPC G4 microprocessor and the Intrepid 2 IC, which provides the functions of a memory controller and an I/O device controller.

The PowerPC G4 microprocessor is connected to the Intrepid 2 IC by a MaxBus. The bus clock speed is 167 MHz. Additional buses implemented by the Intrepid 2 IC are summarized in Table 2-1, which is in the section Intrepid 2 Controller Functions and Buses.

The Intrepid 2 IC has a 32-bit PCI bus with a bus clock speed of 33 MHz. The PCI bus also connects to the Boot ROM, the CardBus controller, and AirPort Extreme. The Intrepid 2 IC has other buses that connect with the hard disk drive, the optical drive, the power controller IC, the audio IC, and the internal modem module.

Each of the components listed here is described in one of the following sections.

PowerPC G4 Microprocessor

The PowerPC G4 microprocessor used in the 15-inch PowerBook G4 has many powerful features, including an efficient pipelined system bus called MaxBus.

Features of the PowerPC G4 include

• 32-bit PowerPC implementation

• superscalar PowerPC core

• Velocity Engine (AltiVec technology): 128-bit-wide vector execution unit

• dual 32 KB instruction and data caches

• an on-chip level 2 (L2) cache consisting of 512 KB with a clock speed ratio of 1:1

• high bandwidth MaxBus (also compatible with 60x bus)

• fully symmetric multiprocessing capability

The PowerPC G4 microprocessor in the 15-inch PowerBook G4 runs at a clock speed of 1.67 GHz.

Level 2 Cache

The data storage for the L2 cache consists of 512 KB of fast static RAM that is built into the microprocessor chip along with the cache controller and tag storage. The built-in L2 cache runs at the same clock speed as the microprocessor.

System RAM

The memory subsystem in the 15-inch PowerBook G4 supports two slots for 200-pin, PC2-4200 DDR2 SDRAM SO-DIMMs (small-outline dual inline memory modules) running at 333 MHz. The data bus to the RAM and DIMM is 64 bits wide, and the memory interface is synchronized to the MaxBus bus interface at 167 MHz. See RAM Expansion Slots.

Boot ROM

The boot ROM is connected to the Intrepid 2 IC by way of the high byte of the PCI bus plus three additional control signals: chip select, write enable, and output enable. The boot ROM is a 1 MB by 8 bit device.

FireWire Controller

The Intrepid 2 IC FireWire controller supports IEEE 1394a FireWire 400 for a maximum data rate of 400 Mbps (50 MBps) and IEEE 1394b FireWire 800 for a maximum data rate of 800 Mbps (100 MBps). The Intrepid 2 IC provides DMA (direct memory access) support for the FireWire interface.

The controller in the Intrepid 2 IC implements the FireWire link layer. A physical layer IC, called a PHY, implements the electrical signaling protocol of the FireWire interface and provides the electrical signals to the port. For more information, see FireWire Ports.

Ethernet Controller

The Intrepid 2 IC includes an Ethernet media access controller (MAC) that implements the link layer. The Intrepid 2 IC provides DB-DMA support for the Ethernet interface.

The Ethernet controller in the Intrepid 2 IC is connected to a PHY interface IC that provides the electrical signals to the port. The PHY is capable of operating in either 10BASE-T, 100BASE-T, or 1000BASE-T mode. The actual speed of the link is automatically negotiated by the PHY and the hub or switch to which it is connected. For more information, see Ethernet Port.

The PHY supports Auto-MDIX, which allows the use of straight-through cables in crossover situations (and conversely). For more information, see Ethernet Port.

Video Display Subsystem

The video display subsystem contains the graphics controller IC with 128 MB memory with dual link DVI functionality. The ATI Mobility Radeon 9700 graphics IC contains 2D and 3D acceleration engines, front-end and back-end scalers, a CRT controller, and an AGP4x bus interface with bus master capability.

The features of the ATI Mobility Radeon 9700 include

• support for 128 MB of DDR video memory with dual link DVI functionality and 128-bit interface

• 2D and 3D graphics acceleration

• transform acceleration

• lighting acceleration

• video acceleration

• support for MPEG decoding

• support for video mirror mode

• support for dual-display mode

• S-video output for a TV monitor

• support for programmable pixel and vertex shading

The interface between the graphics IC and the rest of the system is an AGP4x bus on the Intrepid 2 IC. To give the graphics IC fast access to system memory, the AGP bus has separate address and data lines and supports deeply pipelined read and write operations.

The graphics IC uses a graphics address remapping table (GART) to translate AGP logical addresses into physical addresses. The graphics driver software can allocate memory in both the graphics SDRAM and the main memory.

The graphics IC supports the built-in flat-panel display and an external monitor. The external monitor can either mirror the built-in display or show additional desktop space (dual-display mode). For information about the displays and supported resolutions, see Flat-Panel Display and External Monitors.

DMA Support

The Intrepid 2 IC provides DB-DMA (descriptor-based direct memory access) support for the following I/O channels:

• Ultra DMA ATA interface to the the internal hard drive

• I2S interface to the built-in modem

• I2S channel to the audio IC

The DB-DMA system provides a scatter-gather process based on memory resident data structures that describe the data transfers. The DMA engine is enhanced to allow bursting of data files for improved performance.

Interrupt Support

The Intrepid 2 IC has an interrupt controller (MPIC) that handles interrupts generated within the IC as well as external interrupts, such as those from the Ethernet and FireWire controllers.

USB Interface

The internal USB 1.1 devices are connected via the PCI USB controller; see PCI USB 2.0 Controller.

Ultra DMA/100 Interface

The Intrepid 2 IC provides an Ultra DMA/100 channel that is connected to the internal hard disk drive. The Intrepid 2 IC provides DB-DMA (descriptor-based direct memory access) support for the Ultra DMA interface. The internal hard disk drive is connected as cable-select in an ATA Device 0/1 configuration. For more information, refer to Hard Disk Drive.

The SuperDrive and optional Combo drive are ATAPI drives and are cable-selected in an ATA device configuration. For more information, refer to Combo Drive and SuperDrive.

Modem Support

The internal modem is connected to an internal I2S port. The Intrepid 2 IC provides DB-DMA support for the modem interface. The modem provides digital call progress signals to the audio circuitry.

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.

Audio Circuitry

The audio circuitry is connected to the Intrepid 2 IC by a standard I2S (inter-IC sound) bus. The Intrepid 2 IC provides DB-DMA (descriptor-based direct memory access) support for the I2S port.

The audio circuitry includes a signal processing IC that handles the equalization and volume control functions and a codec IC that performs A-to-D and D-to-A conversion.

All audio is handled digitally inside the computer. The audio circuitry performs digital-to-analog conversion for the audio signals to the internal speakers.

For a description of the features of the audio system, see Audio System.

Power Controller

The 15-inch PowerBook G4 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 24.3K ohms (+/- 1%) connected between the power plug's shell and ground.

The 15-inch PowerBook G4 has a variable speed fan control circuit and a thermal circuit that will force the unit to sleep and slow down the processor if the processor temperature exceeds 85 degrees Celsius. The circuit remains active during sleep so that it can continue to poll the temperature.

The power management controller is a custom IC (PMU05), which controls the Sudden Motion Sensor (SMS), ambient light sensor (ALS), keyboard backlit LED, and the sleep LED. When the 15-inch PowerBook G4 is on and the LCD is off, the sleep LED emits a steady light (no pulsing) to indicate power to the system.

The PMU05 also supports several power-saving modes of operation, including idle, doze, and sleep. For more information, see Power Management.

The process to reset the PMU is listed below.

1. If the computer is on, turn it off.

2. Disconnect the AC Adapter and remove the battery.

3. Press and hold down the power button for 5 seconds, and then release.

4. Wait 5 seconds.

5. Connect the battery and AC Adapter.

6. Press the power button to restart the computer.