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 systemsContinuing 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 slotsCardBus 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.2
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 conflictsLaptop 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 operationThe 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 removalHot 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 considerationsCardBus 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
managementCardBus 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
managementIn 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.6The 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
eventsA 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 packetsThe
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 PacketIn 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 4.0Microsoft 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
2000Windows 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
systemsMany 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 servicesUsers 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