Compaq 8000 Technical Reference Guide: HP Compaq 8000 Elite Series Business De - Page 35

4 System Support 4.1 Introduction This chapter covers subjects dealing with basic system architecture and covers the following topics: ■ PCI bus overview (4.2) ■ System resources (4.3) ■ Real-time clock and configuration memory (4.4) ■ System management (4.5) ■ Register map and miscellaneous functions (4.6) This chapter covers functions provided by off-the-shelf chipsets and therefore describes only basic aspects of these functions as well as information unique to the systems covered in this guide. For detailed information on specific components, refer to the applicable manufacturer's documentation. 4.2 PCI Bus Overview ✎ This section describes the PCI bus in general and highlights bus implementation for systems covered in this guide. For detailed information regarding PCI bus operation, refer to the appropriate PCI specification or the PCI web site: www.pcisig.com. These systems implement the following types of PCI buses: ■ PCI 2.3 - Legacy parallel interface operating at 33-MHz ■ PCI Express - High-performance interface capable of using multiple TX/RX high-speed lanes of serial data streams 4.2.1 PCI 2.3 Bus Operation The PCI 2.3 bus consists of a 32-bit path (AD31-00 lines) that uses a multiplexed scheme for handling both address and data transfers. A bus transaction consists of an address cycle and one or more data cycles, with each cycle requiring a clock (PCICLK) cycle. High performance is achieved during burst modes in which a transaction with contiguous memory locations requires that only one address cycle be conducted and subsequent data cycles are completed using auto-incremented addressing. Devices on the PCI bus must comply with PCI protocol that allows configuration of that device by software. In this system, configuration mechanism #1 (as described in the PCI Local Bus specification Rev. 2.3) is employed. Technical Reference Guide www.hp.com 4-1