In 1995, long before the ETX form factor and the COM Express standard evolved, DIGITAL-LOGIC developed the first Computer On Module (COM). At that time, a bonded Pentium MMX166MHz with a bonded chipset was placed on a module (60 x 68mm).

All subsequent COMs increased in size, culminating with the extended COM Express (110 x 155mm). Intel's energy-saving Atom, a chipset together with a CPU, offers interesting possibilities for embedded computer applications (Table 1, below).

The Atom offers new interfaces and does away with parallel bus systems (ISA, PCI); it is suitable for battery-operated and fanless computer systems. Miniaturization using mini-BGAs with 0.4mm pitch distance requires the use of more expensive HDI printed circuit boards.

Table 1. Atom signals and COM Express requirements

The new smartCore Express format is the size of a business card (58 x 65mm, height = 11mm) and possesses a 220 pin connector link to the printed circuit board as well as a standardized thermal interface (Figure 1, below). This allows operation in an extended temperature range of -40 up to +85 degrees Cetigrade.

At the same time, the CPU, DDR2 memory (up to 2GByte) and the chipset are glued to the PCB by means of underfilling so that the smartCore Express module will be resistant to vibration and shock.

An ordering option is a solid-state drive with 4GByte capacity which allows booting from a fast flash drive. Other embedded computer manufacturers already offer a compatible second source for the smartCore Express.

Figure 1. An open SMA200 unit

The smartCore Express consolidates the minimum number of interfaces which are available from the Atom5x0 with the US15W chipset. The customer can achieve all expansions on the printed circuit board (i.e., LAN, sound, FireWire, VGA, and PCI32bit).

There is always the possibility of incompatibilities with an Atom design on a COM Express module since some signals from the Atom are not made available. Be very careful when onboard functions such as LAN and SATA reduce the number of available free PCIe lanes to almost 0, respectively through the use of PCIe switches the bandwidth of the duplicated PCIe lanes are reduced.

Implementing the Atom design on a smartCore Express module gives a very small and cost-effective printed circuit board (Figure 2 below). The same 220pin connector is used as on the COM-Express. This has the advantage that the connector is available for longer and can be manufactured in large quantities.

Figure 2. The SMA200 with the 1.6 GHz Atom CPU and up to 2 Gbyte of DRAM

The module is screwed on to the carrier board with 4 bolts. All the functions of a normal PC can be found on the module including a robust, soldered-on 2Gbyte memory, a bootable solid-state disk and all voltage generators. The module only requires 5Volts with a typical power input of 5 Watts.

The cover has 4 threaded holes to allow the module to be mounted onto a casing or to mount a passive cooler onto the module. The smartCore Express is small enough that it fits onto a standard PCI/104-Express card.

It leaves space so all the necessary bridges and controllers can be fitted which allows the availability of the functions SATA, PCI32bit, LAN, COM1-4, LPT, back-up battery and PCIe mini-card on a space of only 90 x 96mm. Peripheral expansion is done using the PCI-bus (up to 4 cards) or via the high performance PCI/104-Express bus (up to 4 cards).

PCI/104-Express boards fitted with the latest energy-efficient Intel Atom processors allow for passively cooled operation in the extended temperature range of -40 up to +85 degrees Centigrade.

To simplify the development phase, DIGITAL-LOGIC offers a development kit containing all necessary information, diagrams, tools, implementation guide and support.

Table 2 below shows a comparison of the other COM products on the market which make use of the new, energy-efficient Atom from Intel. The large variations of the functions makes the COM Express solutions less compatible and, prior to each application, the user must find a compromise between functions and number of PCIe lanes.

The Atom based COM Express products are not truly compatible with the previous COM Express products (915 / 945 / 965). From the customer's point of view such implentations do more harm than good.

Table 2. A comparison of COM products which use the Atom CPU from Intel.

Every additional function (i.e., LAN, SATA, VGA, PCI32bit) on the COM raises the power consumption approx. 1 Watt. Since future Atom generations/variations will presumably again include LAN and will probably only have SATA interfaces, the smartCore Express already has reserved pin definitions for just such changes.

Additionally to the COM Express definition, the smartCore Express concept has extra connector pins for SSD/MC cards, SDVO and SPI signals. All technical information for the new smartCore Express specifications and for Atom-based embedded computer products may be downloaded free of charge at www.digitallogic.com.

Felix Kunz is the Chief Executive Officer at DIGITAL-LOGIC AG.