Design Considerations for Migrating Intel386™ and Intel486™ Processor Embedded Systems to the Pentium® Processor Application Note August 1998 Order Number: 273192-001 Information in this document is provided in connection with Intel products. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Intel's Terms and Conditions of Sale for such products, Intel assumes no liability whatsoever, and Intel disclaims any express or implied warranty, relating to sale and/or use of Intel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. Intel products are not intended for use in medical, life saving, or life sustaining applications. Intel may make changes to specifications and product descriptions at any time, without notice. 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Application Note Design Considerations for Migrating to the Pentium® Processor Contents 1.0 Introduction ..................................................................................................................5 2.0 Intel386™ Processor System Overview............................................................6 2.1 Block Diagram .......................................................................................................6 2.2 System Kernel.......................................................................................................7 2.3 Memory Subsystem...............................................................................................7 2.3.1 DRAM.......................................................................................................7 2.3.2 System ROM ............................................................................................7 2.4 ISA Bus Subsystem...............................................................................................8 2.4.1 Address Decoding Logic ..........................................................................8 2.4.2 X-Bus........................................................................................................8 3.0 Intel486™ Processor System Overview............................................................9 3.1 Block Diagram .......................................................................................................9 3.2 CPU Subsystem ..................................................................................................10 3.3 Memory and ISA Subsystem...............................................................................10 4.0 Pentium® Processor System Overview ..........................................................11 4.1 Block Diagram .....................................................................................................11 4.2 Pentium® Processor Design Considerations.......................................................12 4.2.1 Pinout Considerations ............................................................................12 4.3 Northbridge Subsystem.......................................................................................13 4.3.1 TXC System Controller...........................................................................13 4.3.1.1 PCI Interface .............................................................................13 4.3.1.2 Integrated Cache Controller ......................................................13 4.3.1.3 DRAM Interface.........................................................................14 4.3.1.4 Clock Generation.......................................................................15 4.3.2 PCI Bus ..................................................................................................15 4.3.2.1 PCI Bus Features ......................................................................15 4.3.2.2 PCI Bus Clock ...........................................................................15 4.3.2.3 PCI Pin Signals .........................................................................16 4.3.2.4 PCI Subsystem Design Considerations ....................................17 4.4 Southbridge Subsystem ......................................................................................19 5.0 Summary......................................................................................................................20 6.0 Related Information.................................................................................................20 Application Note 3 Design Considerations for Migrating to the Pentium® Processor Figures 1 Intel386™ Processor System Block Diagram ....................................................... 6 2 Intel386™ Processor System Memory Block Diagram ......................................... 7 3 Intel486™ Processor Block Diagram .................................................................... 9 4Pentium® Processor System Block Diagram ...................................................... 11 5 256 Kbyte Level-2 Cache with PBSRAM (64 Mbyte Cacheability) ..................... 14 Tables 1 Differences between Pentium® Processors and Pentium Processors with MMX™ Technology ..................................................................................... 12 2 PCI Signal Description ........................................................................................ 16 3 Related Documents............................................................................................. 20 4 Application Note Design Considerations for Migrating to the Pentium® Processor 1.0 Introduction Intel® architecture (IA) processors, from the Intel386™ processor to the Pentium® processor, provide a compelling option for embedded designs. With strong tools support, a robust development environment, and a clearly defined upgrade path, IA is being used in a variety of embedded systems, from point-of-sale (POS) terminals and retail kiosks to advanced networking equipment. Pentium processors are enabling high-end embedded product developers to step up to new levels of performance. The personal computer migrated from the 8-MHz ISA bus architecture in the 80386 microprocessor generation to the 33-MHz VL-bus architecture in the 80486 microprocessor generation. In just a short time, designers adopted the 33- and 66-MHz PCI bus architecture to enable the latest Pentium processor PCs. Embedded system design differs slightly from classic PC system design. Many chip vendors introduced supporting chipsets for 80386 and 80486 microprocessors, that integrated peripherals onto the bus controller and the memory controller. Embedded systems based on these chipsets were easy to implement. However, these designs were often unique and did not possess a smooth upgrade path. This application note is intended to assist embedded systems designers in migrating from previous 80386 or 80486 processor-based designs to higher performance Pentium processor-based designs. This application note can be used with the following documents: 33 MHz 386 System Design Considerations (order number 240725), Intel 430HX PCIset Design Guide (order number 297467), and application note AP-479 Pentium® Processor Clock Design (order number 241574). This application note discusses the bus technologies and design structures for the earlier 80386 and 80486 microprocessor systems and addresses design considerations for migrating to Pentium processor designs. Software considerations, BIOS, and operating system issues are not discussed. Application Note 5 Design Considerations for Migrating to the Pentium® Processor 2.0 Intel386™ Processor System Overview 2.1 Block Diagram Figure 1. Intel386™ Processor System Block Diagram System Kernel Memory Subsystem Host Bus System Microprocessor Memory Cache System Clock Bus Controller ROM DMA Subsystem ISA Subsystem Interrupt Subsystem X-Bus Keyboard ISA Bus Subsystem RTC & Config ISA Expansion RAM Slots ISA Timers 6 Application Note Design Considerations for Migrating to the Pentium® Processor 2.2 System Kernel The CPU subsystem consists of the 80386 microprocessor, the ISA bus controller, and other support logic. The primary function of the bus control logic is to provide the basic signals, timing, and protocols necessary for the microprocessor to communicate with the rest of the system. The bus control logic assists the microprocessor in running bus cycles. There are many bus controllers with integrated peripherals to ease the task of system design. 2.3 Memory Subsystem The memory system