White Paper: The full potential of the CardBus standard can now be realised

Mobile computer developers face an ongoing challenge to match desktop speed, but are constrained by the need for portability and...

Mobile computer developers face an ongoing challenge to match desktop speed, but are constrained by the need for portability and ease of use

CardBus was standardised by the Personal Computer Memory Card International Association (PCMCIA) in May 1996, and is now the preferred high-speed mobile interconnect bus currently shipping on virtually all mobile PCs. CardBus devices combine the mobility of PC Cards with the high performance of 32-bit PCI adaptors.

CardBus delivers increased throughput and functionality by advancing PC Card technology from 16-bit to 32-bit data transfers, bus mastering and other PCI features. In addition, CardBus slots maintain backward compatibility with 16-bit PC Cards. This third generation PC Card technology delivers significant advantages by requiring less power and providing higher data throughput, while maintaining a small form factor, robust operation and ease of use. Xircom's LAN, modem and LAN+modem products are available in both 32-bit CardBus and 16-bit versions.

When combined with Advanced Configuration and Power Interface (ACPI) hardware support, CardBus takes advantage of the enhanced system and power management capabilities provided by Windows 98 Second Edition and Windows 2000, including OnNow power management policies and remote power management features like Wake-on-LAN.

First-generation notebook computers with PC Card slots (formerly known as PCMCIA slots) used variations on the original 16-bit Industry Standard Architecture (ISA) bus. These systems provided data transfers between PC Card slots, memory, disk drives and other system devices at speeds up to 8.33Mbit/s for each slot. Resulting performance closely matched that of the original 8088 and 80286-based PC/XT and PC/AT systems, but proved inadequate as desktop technology moved to 80386 class and faster microprocessor architectures.

A modest improvement, with faster clocking speeds and tighter timing tolerances, was realised by well-designed laptop systems that internally used either Extended ISA (EISA) or Video and Electronics Standards Association (VESA) Local Bus architecture (VL-Bus) with 16-bit PC Card slots. With this approach, data transfers could approach the 20Mbit/s maximum specified by the PCMCIA 2.0 standard. This performance was adequate for devices such as modems, standard Ethernet and Token Ring network adaptors, still video capture devices, and Small Computer System Interconnect (SCSI-1) peripherals. However, the subsequent use of true 32-bit microprocessors and the availability of sophisticated 32-bit operating systems, such as Microsoft Windows 95 and Windows NT, made the limitations of 16-bit bus architectures more acute.

The Peripheral Component Interconnect (PCI) standard first became available in July 1992. It addressed concerns of desktop computer users tired of system bottlenecks caused by fast processors throttled by the slow busses. PCI-based systems finally had a high performance bus with speed in the same range as processor speed, delivering excellent overall system throughput. With desktop systems implementing PCI, it became apparent that portable computer users required a true 32-bit bus solution as well.

CardBus delivers higher bandwidth, lower power and better manageability in mobile systems

Continuing growth in mobile computing technologies and applications has driven the need for higher performance systems and architectures. Examples include:

( High-speed peripheral interfaces such as Fast/Wide SCSI and IEEE 1394 (FireWire) require 32-bit throughput

( Fast Ethernet and other performance-oriented networks can quickly overwhelm traditional 16-bit PC Card slots

CardBus brings the benefits of PCI to the mobile computer platform. It delivers the same 132Mbit/s throughput and provides additional benefits important to mobile users. Like PCI, CardBus in mobile computers significantly contributes toward reducing its Total Cost of Ownership (TCO). The Plug and Play (PnP) capabilities of CardBus enable automatic system configuration upon insertion of the PC Card, reducing the likelihood of configuration errors, thereby increasing user convenience while reducing the frequency of service calls. These benefits make it possible for computer manufacturers to sell CardBus-equipped PCs that are upgradeable via standard PC Cards.


Key CardBus features include:

( True 32-bit I/O with high-speed 33 MHz bus, compared with an 8.33 MHz bus for 16-bit I/O

( Low power consumption using 3.3-volt CMOS devices

( Improved power management with ACPI reduces power consumption and increases notebook battery life

( Hot insertion and automatic configuration (PnP)

( True processor independence

( Bus mastering allows data to be transmitted by adaptor without interrupting the host processor

( Support for 16-bit PC Card and 32-bit CardBus devices in the same slot

( Burst-mode data transfers

( A built-in shared resource capability that improves multifunction card efficiency and reduces compatibility problems

( Improved grounding and shrouded connectors that support higher bus speeds and reduce electromagnetic interference (EMI)

( Support for PCI standard resource steering capabilities (a component of PnP) that simplifies configuration of 16-bit and 32-bit devices by minimising resource conflicts

Laptop manufacturers have quickly adopted CardBus technology since 1997, with more than 98 per cent of laptops shipped in 1998 now supporting CardBus devices.

Low-power operation

The low-power CMOS 3.3-volt technology used with CardBus delivers improved system battery life compared to the 5-volt technology used with 16-bit PC Cards. This improved power requirement enables CardBus adaptors to generate less heat, increasing reliability and performance. The improved grounding provided by the new CardBus cover and shrouded 68-pin connector, supports higher bus speeds, reduces the probability of electromagnetic interference and addresses related limitations of earlier PC Card devices. By design, CardBus devices reduce power consumption and increases notebook battery life.

Hot insertion and removal

Hot swapping enables the PC Card to be gracefully removed and inserted without rebooting the system, or to disconnect the node while the computer is operating. CardBus combines familiar Card Information Structure (CIS) with PCI-derived configuration. Standard PCMCIA configuration software (socket services, card services, and a card device driver) supports the dynamic configuration of CardBus peripherals. This software communicates with the CardBus adaptor through the PCI-to-CardBus bridge.

Mechanical considerations

CardBus adaptors use the same general form factor as 16-bit PC Cards and use the same 68-pin connector to interface with the card slot. Both 32-bit CardBus and 16-bit CardBus peripherals can use Type I (3.3mm), Type II (5.0 mm), or Type III (10.5mm) thickness, depending on the application. The frames and slots used with CardBus devices differ from those used with 16-bit PC Cards. Special keying makes it nearly impossible for a user to insert a CardBus card into a 16-bit slot, while still permitting a 16-bit PC Card to be used in the CardBus slot. The primary difference between CardBus and PC Cards is in the metal cover near the 68-pin CardBus connector. The raised bumps and isolation of this shrouded connector are part of a sophisticated grounding system used exclusively by CardBus devices.

Power management

CardBus technology supports several advanced power management strategies as part of the OnNow power management features available in Microsoft Windows 98 and Windows 2000. Power Management for network media involves putting the system to sleep (suspend) and turning the networking devices to lower power states, or to off, when the network is not in use and then waking up the system (resume), based on user intervention or network traffic directed to the system from the network.

NDIS 5.0 and power management

In order to use a network adaptor in a Microsoft operating system such as Windows 2000, it is necessary to install a software driver for the adaptor that conforms to the Microsoft Network Driver Interface Specification (NDIS). Microsoft has released the NDIS 5.0 specification for use in developing drivers for Windows 98 and Windows 2000. NDIS 5.0 extends previous versions of NDIS. One of the new features is network power management. Support for ACPI and Wake-on-LAN is implemented in NDIS 5.0 drivers. NDIS can power down the network adaptor when the system requests a power level change; a request that can be initiated either by the user or by the system. For example, the user might want to put the system in sleep mode, or the system might request this based on keyboard or mouse inactivity. If supported by the network adaptor, a power down request to a network device can be affected by disconnecting the network cable. In such a case, the system would wait for a configurable time period before powering-down the network adaptor ( the disconnect might be a result of temporary wiring changes on the network, and not necessarily a result of the cable disconnecting from the network device itself.


The NDIS power management policy is "no Net activity"-based, meaning that all overlaying network components must agree to the reset request before the network adaptor can be powered-down. If there are any active sessions or open files over the network, the power down request can be refused by any or all of the components involved. NDIS 5.0 drivers are currently under development for all Xircom CardBus products and are expected to be available in the summer and autumn of 1999.

Network wake-up events

A network wake-up event is a request from hardware or software, external to the portable computer, to put the system into fully powered state from a lower power state. This is commonly referred to as Wake-on-LAN. The PC 99 System Design Guide requires support for Wake-on-LAN for the following network communication devices and their associated NDIS 5.0 miniport drivers:

( Ethernet and Token Ring network adaptors

( Integrated DOCSIS cable modems

( Other devices that transfer 802.3/DIX Ethernet framed packets

The Network Device Class Power Management Reference Specification defines three methods of causing wake-up events:

( Detection of a change in the network link state

( Receipt of a network wake-up frame

( Receipt of a Magic Packet

In addition, other methods can be defined and implemented by manufacturers. Xircom CardBus cards support all three methods. Currently, Wake-on-LAN is not supported for CardBus devices in Windows 98 or 2000, but is expected to be supported in the first service pack to Windows 2000.

Microsoft Windows 95, Windows 98 and Windows NT 4.0

Microsoft Windows 95 OSR2 and later revisions support single function CardBus adaptors. Some manufacturers, including Xircom, have multifunction CardBus products that are compatible with Windows 95 OSR2. This requires the drivers to work around limitations within the operating system. This also requires the user to download the latest system drivers from the Microsoft website.

Microsoft Windows 98 has full built-in support for CardBus products. Microsoft Windows NT 4.0 does not have Plug and Play support for CardBus adaptors, however it is possible to use enabler software built-into drivers or third-party Card and Socket Services to support CardBus devices.

Windows 2000

Windows 2000 is a dramatic leap forward for mobile computer users. Major design goals of Windows 2000 include:

( Create a consistent working environment for mobile computer users whether they are connected or disconnected from the network, enabling them to work more productively

( Improve battery life for mobile systems

Many of the power saving and manageability features being implemented in Windows 2000 will be supported only with CardBus adaptors, and not with 16-bit PC Cards. These features include ACPI and Wake-on-LAN. In Windows 2000, CardBus adaptors are supported only on ACPI-based systems. Most notebooks shipped since late 1998 support ACPI (in some cases a BIOS update may be required). Microsoft is considering adding the CardBus support for legacy, non-ACPI, systems in future Windows 2000 service packs. The support for Power Management is as follows: NOTE: For desktop systems using PCI cards, Power Management and Network Wake-up events are supported.

Enabler, card and socket services

Users of DOS, Windows 3.1x, OS/2 or UNIX environments must use Card and Socket Services (CS/SS) enabler software built into drivers to support CardBus devices. Enabler software is an alternate interface to CS/SS between the PC Card hardware and host system. It saves system memory and reduces potential resource conflicts. Advanced features such as hot-swap, may not be available for CardBus until CS/SS is updated. Revised software is available from notebook manufacturers, operating system vendors, or third parties such as SystemSoft, Award, Softex and others.

Compiled by Mike Burkitt

( Xircom 1999

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