Electronic Design

New Mini-Card Form Factor Embeds PCI Express

Spec release opens door for laptops, embedded systems to exploit PCI Express mini-card products.

Getting on PCI Express just got a little easier for laptops and embedded devices with the release of PCI Express Mini Card Electromechanical Specification Revision 1.0. This compact platform targets standard devices like 802.11x wireless adapters, Bluetooth interfaces, Ethernet adapters, and modems. The PCI mini-card form factor has already found a home in most major laptops, but shifting to PCI Express required a new standard.

Having the 2.5-Gbit/s serial bus in tow means more than just moving up to the latest technology. The mini-card form factor is designed for compact environments. The standard is modeled after the Mini PCI Type III card without the side retaining clips. I/O connectors are restricted to a small area at the end opposite the card connector.

The limited number of pins required for a single-lane PCI Express connection allows for other features, so there's no need for a large edge connector. For example, a Universal Serial Bus (USB) version 2.0 and an SMBus interface can be implemented on a card. The USB interface supports low-speed, full-speed, and high-speed modes. USB devices report as self-powered devices because the standard mini-card power connections supply the power. The SMBus is often used for system management on mobile devices. The primary use of the new form factor will be PCI Express connectivity, but these other interfaces could be used in a standalone configuration that takes advantage of the standard, compact form factor.

Employing standard interfaces like PCI Express and USB enables devices to be supported using normal device drivers. No change in drivers or applications should be required to utilize one of these cards. Advanced power-management support may be augmented through device drivers, but the auxiliary and status communication pins provide a mechanism to improve device and power control.

Although the new standard employs 52 pins, almost a third of these is reserved for future use. Features such as a second PCI Express lane and a Subscriber Identity Module (SIM) interface are noted within the standard. A second lane would double system throughput. SIMs often found in wireless devices allow for easy implementation of configuration and security information.

By having this new standard well in advance of general PCI Express product availability, designers can incorporate a flexible interface that will handle a wide range of peripherals. These range from low-speed modems to wired and wireless, high-speed network interfaces.

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