Information Technology Reference
In-Depth Information
5
Motherboard Design
5.1
Introduction
This chapter analyses a Pentium-based motherboard. An example board is the Intel 430HX
motherboard which supports most Pentium processors and has the following component
parts:
•
PCIset components - 82438 System Controller (TXC) and 82371SB PCI ISA Xcelerator
(PIIX3).
•
82091AA (AIP) for serial and parallel ports, and floppy disk controller.
•
DRAM main memory.
•
L2 cache SRAM.
•
Universal serial bus (USB).
•
Interface slots (typically 4 PCI and 3 ISA).
•
1 Mbit flash RAM.
Figure 5.1 illustrates the main connections of the PCIset (which are the TXC and PIIX3 de-
vices). The TCX allows for a host-to-PCI bridge, whereas the PIIX3 device supports:
•
PCI-to-ISA bridge.
•
Fast IDE.
•
APIC interface.
•
USB host/hub controller.
•
Power management.
The 430HX board has 3 V and 5 V busses. PCI bus connections are 5 V and the Pentium bus
is 3V.
5.1.1 Pentium-II/III processor
Figure 5.2 illustrates the main connections to the Pentium II/III processor. It can be seen that
it has:
•
64-bit data bus (D0-D63) which connects to the TXC (HD0-HD63).
•
32-bit address bus (A0-A31) which connects to the TXC (HA0-HA31).
•
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 (M/IO#) which connects to TXC (HM/IO#).
•
Data/control (D/C#) which connects to TXC (HD/C#).
