Abstract:
In accordance with an embodiment of the present invention, a computer system allows an expansion component of the computer system to properly operate even when the computer system is in a low-power mode. According to an embodiment of the present invention, a local system bus has a first section and a second section. An isolation circuit is included which selectively establishes a connection between the first section of the local system bus and the second section of the local system bus during a normal-power mode of the computer system and removes the connection between the first section of the local system bus and the second section of the local system bus during a low-power mode.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an isolation circuit in a computer system. More particularly, the present invention relates to an isolation circuit enabling an expansion component to operated properly in a low-power mode. 
     BACKGROUND OF THE INVENTION 
     A computer system supplied by a computer manufacturer typically includes a main to printed circuit board (commonly referred to as the “motherboard”) on which fixed system components are mounted. These fixed system components may include a microprocessor (as referred to as a processor), random access memory (RAM), read only memory (ROM), expansion slots, etc. Linking all of these fixed system components that are mounted onto the motherboard are a series of system buses. One particular system bus included on the motherboard is the local system bus. The local system bus is a bus used by the microprocessor. One advantage of the local system bus is that it may communicate with the microprocessor at the microprocessor&#39;s speed, which typically is the fastest operating fixed system component. 
     Another type of system component located on the motherboard is an expansion component. Expansion components are used to provide additional functionality to the computer system. Thus, when the local system bus is connected between the microprocessor and another system component, such as the expansion slots with expansion components like video and drive controller cards attached thereto, the overall performance of the expansion component is greatly enhanced. 
     In order for the computer system to operate, a power supply is coupled to the motherboard to supply power. The power supply sends power to all of the other system components through its own bus. With an increasing popularity of mobile computers, as evidenced by a growth in a market for so-called “notebook” or “laptop” computers, power consumption has become an important consideration for computer designers. Power conservation efforts have been directed at virtually every aspect of such computers, including hardware, firmware and software. For example, most of today&#39;s popular processors, such as Intel&#39;s Pentium® family of processors, are capable of operating in a low-power mode. In addition, many computer systems now include power management functionality as part of an installed BIOS (Basic Input-Output System). Software developers are also becoming more power-conscious, writing “green” applications which are themselves power efficient while cooperating with the aforementioned hardware and firmware facilities. 
     One of the problems faced by computer designers, firmware developers and software developers with respect to power management is the use of expansion components that require power when the computer system is in a low power state. For example, expansion components may include monitoring circuitry used to monitor the temperature or the voltage of the computer system when the computer system is operating in a normal-power mode or in a low-power mode. This monitoring circuitry provides information to a remote location which can be part of a local area network (LAN). 
     When the computer system operates in a low-power mode, most fixed system components are switched off and the microprocessor is either switched off or operates at reduced power. However, expansion components connected to same local system bus as the switched off fixed system components, are negatively affected by these components because the switched off component may drain power from the local system bus. 
     There is presently no satisfactory solution to the problem of an expansion component properly operating when the computer system is in a low-power mode. 
     SUMMARY OF THE INVENTION 
     In accordance with an embodiment of the present invention, a computer system allows an expansion component of the computer system to operate even when the computer system is in a low-power mode. According to an embodiment of the present invention, a local system bus includes a first section and a second section. An isolation circuit is included which selectively establishes a connection between the first section of the local system bus and the second section of the local system bus during a normal-power mode of the computer system and removes the connection between the first section of the local system bus and the second section of the local system bus during a low-power mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood to those skilled in the art by reference to the following drawing, in conjunction with the accompanying specification, in which: 
     FIG. 1 is a block diagram illustrating a computer system in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In accordance with an embodiment of the present invention, a computer system allows an expansion component of the computer system to operate even when the computer system is in a low-power mode. According to an embodiment of the present invention, the computer system includes a local system bus connected between a processor and an expansion component and an isolation circuit electrically separating the local system bus into a section connected to the processor and a section connected to the expansion component such that during a normal-power mode, the section connected to the expansion component and the section connected to the processor are coupled together and during a low-power mode, the section connected to the expansion component and the section connected to the processor are isolated from each other. 
     The section of the local system bus connected to the processor also includes fixed system components that are powered down, i.e., switched off during the low-power mode. Alternatively, the section of the local system bus connected to the expansion component includes system components that require power when the computer system is in the low-power mode. Because the switched off system components negatively affect the local system bus, rendering it unusable during the low-power mode, the isolation circuit is provided to electrically separate the local system bus. Therefore, the negative interference of the switched off system components is eliminated. 
     FIG. 1 is a block diagram representation of a computer system architecture in accordance with an embodiment of the present invention. Computer system  100  includes a motherboard  105  on which system components such as microprocessor or processor  110 , network adapter  190 , monitoring circuit  180 , expansion slots  130 - 133  and system devices  120 - 122  are located. Computer system  100  is controlled primarily by computer readable instructions, which can be in the form of software, wherever, or by whatever means such software is stored or accessed. Such software may be executed with the microprocessor  110  to cause computer system  100  to do work. 
     Each of the system components is connected to a local system bus. The local system bus is electrically separated into two sections, system bus  111  and Peripheral Component Interconnect (“PCI”) system bus  160 , the PCI Local Bus revision 2.1, of PCI Special Interest Group, located in Portland, Oregon. An isolation circuit  150  is used to electrically separate the local system bus into system bus  111  and PCI system bus  160 . Isolation circuit  150  includes a field effect transistor (FET). The FET is controlled by a power supply “power-good signal.” Besides the voltages and current computer system  100  needs to operate, the power supply provides a power-good signal to tell computer system  100  that all is well with the power supply and the computer can operate normally. 
     System devices  120  and  121  are coupled to system bus  111 . These system devices include Dual In-line Memory Modules (DIMM)  120  for accommodating random access memory (RAM) and read only memory (ROM) and clock buffer  121 . Although only two system devices are shown, other system devices may be used without departing from the scope of the present invention. 
     An expansion card or board is a circuit board that includes chips and other electronic components and circuitry connected that add functions or resources to computer system  100 . Typically expansion cards add memory, disk-drive controllers, video support, parallel and serial ports, and internal modems. The expansion cards may include Peripheral Component Interconnect (PCI) cards, Video Electronics Standards Association (VESA) cards, as well other types of expansion cards. 
     According to one embodiment of the present invention, an expansion card includes a monitoring circuit that monitors the status of computer system  100 . For example, the monitoring circuit monitors the temperature of the system components to determine if the temperature of the system components exceeds a predetermine value. Thus, the monitoring circuit would prevent the computer from overheating. In addition, the monitoring circuit monitors voltage supplied to the system components to determine whether the supplied voltage exceeds a predetermined threshold. Other types of monitoring circuits may be used to monitor various events regarding computer system  100 . Thus expansion slots  130 - 133  connected to PCI system bus  160  may be used to receive various types of expansion cards such as an expansion card containing the monitoring circuit. Alternatively, and as shown in FIG. 1, the monitoring circuit  180  may be directly connected to PCI system bus  160 . 
     Also connected to PCI system bus  160  is network adapter  190 . Network adapter  190  may be used to connect computer system  100  to a local area network (LAN)  195 . LAN  195  may provide computer system  100  users with a means of communicating and transferring software and information electronically. Additionally, LAN  195  may provide distributed processing, which involves several computers in the sharing of workloads or cooperative efforts in performing a task. According to an embodiment of the present invention, network adapter  190  is used to report the results from the monitoring circuit  180  to LAN  195 . 
     In order to manage the power used by system components, the computer system may operate according to the Advanced Power Management (APM) interface specifications (APM BIOS Interface Specification, version 1.2, February 1996) is incorporated to control system component power saving features with software control. APM is an overall computer system feature. Although it has the ability to individually control features of each of the system components it manages, APM also controls all system features together to conserve power. APM provides for power savings at five levels: 
     Full On mode—the computer system is operating at full or normal power with all system components running in their normal full power consumption modes. 
     APM Standby mode—the microprocessor may stop and many of the system components are turned off or operate at reduced power. The computer system usually cannot process data, but its memory is kept alive and the status of all system components is preserved. 
     APM Suspended mode—the computer system shifts to its maximum power saving mode-most system components are switched off and the microprocessor switches to its lowest power state with its clock turned off. 
     Hibernation mode—is a special implementation of the suspend mode that allows the computer system to be switched entirely off and still be restored to the point at which it entered the suspend stated. When entering the hibernation mode, the computer system copies memory and other status data to nonvolatile storage such as the hard disk which allows for memory power to be switched off. 
     Off mode—power to the computer system is entirely off. 
     According to an embodiment of the present invention, when computer system  100  is operating in the normal mode, all system components are fully operating. In addition, system bus  111  is electrically connected to PCI system bus  160 . Thus, each of the system components is fully operable and can communicate with each other and with external components. 
     When computer system  100  is in a low-power mode such as the APM Standby, APM Suspended or Hibernation modes, however, system components connected to system bus  111  are either powered down or switched off. The switched off system components negatively affect the system bus rendered unusable during the low-power mode. Alternatively, system components connected the PCI system bus  160  still require power when computer system  100  operates in this mode. The isolation circuit is provided to electrically separate the system bus  111  from PCI system bus  160 . Therefore, the negative interference from the powered off system components is eliminated and the expansion components requiring power can operate in a normal fashion. 
     Several embodiments of the present invention are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations of the embodiments of the present invention are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.