Block Diagram

Figure 2-1 is a simplified block diagram of the main logic board. The diagram shows the input and output connectors, the main ICs, and the buses that connect them together.

Main ICs and Buses

The architecture of the 12-inch PowerBook G4 is designed around the PowerPC G4 microprocessor and the custom Intrepid memory and I/O controller. The Intrepid IC occupies the center of the block diagram.

The microprocessor is connected to the Intrepid IC by a MaxBus with 64 data lines and a bus clock speed of 167 MHz. The Intrepid IC has other buses that connect with the Boot ROM, the main system RAM, the graphics IC, and the Ethernet and FireWire PHY ICs. Each of the components listed here is described in one of the following sections. The buses implemented by the Intrepid IC are summarized in Table 2-1, which is in the section Intrepid Memory and I/O Device Controller.

Power PC G4 Microprocessor

The microprocessor used in the 12-inch PowerBook G4 is a PowerPC G4. It has several features that contribute to superior performance, including:

• on-chip level 1 (L1) caches, 32 KB each for instruction cache and data cache

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

• a microprocessor core optimized for Mac OS applications

• 32-bit PowerPC implementation

• superscalar PowerPC core

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

• high bandwidth MaxBus with 36 address bits and 64 data bits

The G4 microprocessor in the 12-inch PowerBook G4 normally runs at a clock speed of 1.5 GHz. The power saving feature slows the CPU clock speed to save power when the computer is idle. See Power Management.

L2 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. The built-in L2 cache runs at the same clock speed as the microprocessor.

System RAM

The memory subsystem in the 12-inch PowerBook G4 consists of 256 MB of DDR333 (PC2700) SDRAM soldered on the main logic board and 256 MB DDR333 (PC2700) SO-DIMM in the expansion slot. RAM is expandable by 1 GB DDR SO-DIMM in the expansion slot for a total of 1.25 GB of system RAM.

The data bus to the RAM and SO-DIMM is 64 bits wide, and the memory interface is synchronized to the MaxBus interface at 167 MHz. See also RAM Expansion.

Boot ROM

The boot ROM includes the hardware-specific code and tables needed to start up the computer, to load an operating system, and to provide common hardware access services.

The boot ROM is connected to the PCI interface of the Intrepid IC. The boot ROM is a 1 M by 8 bit flash device and can be updated in the field.

Ethernet Controller

The Intrepid IC includes an Ethernet media access controller (MAC) that implements the link layer. As a separate channel connected directly to the Intrepid logic, it can operate at its full capacity without degrading the performance of other peripheral devices. The Intrepid IC provides DB-DMA support for the Ethernet interface.

The controller is connected to a PHY interface IC that is capable of operating in either 10-BaseT or 100-BaseT mode. The actual speed of the link is automatically negotiated by the PHY and the bridge or router to which it is connected. For information about the connector and the operation of the port, see Ethernet Port.

FireWire Controller

The Intrepid IC includes an IEEE 1394a FireWire 400 controller with a maximum data rate of 400 Mbps (50MBps). The Intrepid IC provides DMA (direct memory access) support for the FireWire interface. The FireWire 400 controller complies with the Open Host Controller Interface (OHCI) specification.

The controller IC implements the FireWire link layer. A physical layer IC, called a PHY, implements the electrical signalling protocol of the FireWire interface. The PHY is the interface to the external connector. For information about the connector and the operation of the port, see FireWire 400 Port.

Graphics IC

The graphics IC is an nVidia GeForce FX Go5200 with 64 MB of graphics DDR SDRAM. It provides video for both the internal flat panel display and an external video display. The signals to the external display can be either VGA, composite video, or S-video; for more information, seeExternal Display Port.

The nVidia GeForce FX Go5200 graphics IC in the 12-inch PowerBook G4 supports a display size of 1024 by 768 pixels, with lesser resolutions scaled accordingly.

ThenVidia GeForce FX Go5200 IC also has a 3D graphics engine for fast rendering of 3D objects.

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 more information, see Flat-Panel Display and Extended Desktop Display and Mirror Mode.

Because the graphics IC uses the AGP bus, it can use part of main memory as additional graphics storage. The computer’s virtual memory system organizes main memory as randomly-distributed 4 KB pages, so DMA transactions for more than 4 KB of data would have to perform scatter-gather operations. To avoid this necessity for graphics storage, the AGP logic in the Intrepid IC uses a graphics address remapping table (GART) to translate a linear address space for AGP transactions into physical addresses in main memory.

EIDE Bus

The Intrepid IC provides an EIDE bus that is connected to the Combo or SuperDrive optical drive. The optical drive is connected as device 0 (master). Digital audio data from the CD or DVD drive is processed by the Sound Manager and then sent out through the Intrepid IC to the sound IC.

Ultra ATA-100 Bus

The Intrepid IC provides an Ultra ATA-100 channel that is connected to the internal hard disk drive. The Ultra ATA interface has a data tranfer rate of ATA-100 and is ATA-6 compatible. The Intrepid IC provides DB-DMA (descriptor-based direct memory access) support for the Ultra ATA interface. The internal hard disk drive is connected as device 0 (master) in an ATA Device 0/1 configuration.

USB Interface

The Intrepid IC has three independent USB Open Host Controller Interface (OHCI) controllers. One each is used for the Bluetooth interface and trackpad and the third one is not used.

The external USB interface is via the PCI USB 2.0 controller; see PCI USB 2.0 Controller.

Modem Support

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

The internal modem is a separate module that contains the datapump IC and the interface to the telephone line (DAA). The controller functions are performed by the main processor. See Internal Modem.

Sound Circuitry

The 12-inch PowerBook G4’s sound circuitry is connected to the Intrepid IC by a standard I2S bus. The Intrepid IC provides DB-DMA (descriptor-based direct memory access) support for the I2S port.

The sound 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 sound circuitry performs digital-to-analog conversion for the audio signals to the three internal speakers and the headphone mini-jack. The mid-range enhancer speaker is internal to the unit and is not visible. All audio signal conditioning is done in hardware and no user-level controls exist. The sound circuitry also provides parametric equalization for the internal speakers.

Modem progress audio is connected as a digital input to the sound circuitry so that it can be mixed into the sound output stream. The modem progress audio is processed as play-through only, not as a digital sound source.

Stereo signals from the audio input jack are routed to an analog line input buffer that drives the internal A/D converter. For information about sound system operation, see Sound System.

Power Control IC

The power manager IC in the 12-inch PowerBook G4 is a Mitsubishi M16C/62F microprocessor, also called the PMU99. It operates with its own RAM and ROM. The functions of the PMU99 include:

• controlling the sleep and power on and off sequences

• real time clock

• controlling power to the other ICs

• monitoring the battery charge level

• controlling battery charging

• supporting the interface to the built-in keyboard

The 12-inch PowerBook G4 can operate from a 15-volt power outlet on an airliner, however 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 connected between the power plug's shell and ground.

The PMU99 also provides the hardware interface to the keyboard. Software in the PMU99 IC scans the keyboard, then sends the data to the system in packets like those from the ADB. To the system, the keyboard behaves as if they were ADB devices.

Sudden Motion Sensor

The Sudden Motion Sensor (SMS) helps to detect an accidental drop or fall by sensing a change in position and accelerated movement of the 12-inch PowerBook G4. In the event of a drop, the Mobile Motion Module instantly parks the hard drive heads to help lessen the risk of damage to the hard drive on impact. When the Mobile Motion Module senses that the PowerBook position is once again stable, it unlocks the hard drive heads and the system is up and running within seconds.