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11

Motherboard Design

11.1 Introduction

This chapter analyzes a Pentium-based motherboard. An example board is the Intel 430HX motherboard that supports most Pentium processors and has the following com- ponent parts:

  • PCIset components. 82438 System Controller (TXC) and 82371SB PCI ISA Xcel-

erator (PIIX3).

  • 82091AA (AIP) for serial and parallel ports, and floppy disk controller.

  • DRAM main memory. These are arranged either as SIMMs or DIMMs.

  • L-2 cache SRAM. Support for up to 256kB level-2 cache.

  • Universal Serial Bus (USB).

  • Interface slots (typically 4 PCI and 3 ISA).

  • 1 Mbit flash RAM.

Figure 11.1 illustrates the main connections of the PCIset (which are the TXC and PIIX3 devices). The TXC allows for a host-to-PCI bridge, whereas the PIIX3 device supports:

  • PCI-to-ISA bridge.

  • Fast IDE.

  • APIC (Advanced Programmable Interrupt Controller) support.

  • USB host/hub controller. Connection to the Universal Serial Bus.

  • Power management.

The 430HX board has 3 V and 5 V busses. PCI bus connections are 5 V and the Pentium bus is 3 V. An upgraded TX board includes the upgraded 82439 System Controller (MTXC) and the 82371AB PCI ISA Xcelerator (PIIX4).

11.2 Pentium processor

Figure 11.2 illustrates the main connections to the Pentium II processor (note that a # symbol after the signal name identifies an active low signal). It can be seen that it has:

  • 64-bit data bus (D0D63) which connects to the TXC (HD0HD63).

  • 32-bit address bus (A0A31) which connects to the TXC (HA0HA31).

  • 8-byte address lines (BE0 BE7 ) to allow the processor to access from 1 to 8 bytes

(64 bits) at a time, which connects to TXC ( HBE0 HBE7 ).

  • Read/write line ( W / R ) which connects to TXC ( HW / R ).

  • Memory/IO ( HM / IO ) which connects to TXC ( HM / IO ).

  • Data/control ( HD / C ) which connects to TXC ( HD / C ).

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