Embedded Pentium® Processor-Based POS Terminal Sample Design

A fence is a line routed out of a plane such that a given area is isolated from the rest of the plane except at a single point of contact, conceptually the “gate” in the fence. A fence will minimize noise originating from the digital signaling onto the analog signals. This provides higher quality video or audio. An example is shown in Figure 1. The heavy black line is the routed area. The width of the gate or opening can be up to 75% of the length of the integrated circuit or signals in question. The width of the routed fence should conform to the separation routing between power planes (i.e., 25 mils minimum).

Figure 6. Fence Example

Routed “fence”

Fenced area

Overlying

Chip/Signals

“gate”

Plane (e.g., VCC)

8.0Windows CE

Windows CE can have the same look and feel as Microsoft Windows 98 or Windows NT. A variety of interfaces are supported for embedded applications. The hardware configuration for an embedded system can include the following peripherals: keyboard, mouse, touch screen, and so forth. It is often easier for users to deal with commands and keys that pertain to the desktop PC because they are familiar to dealing with them on their office or home desktop PC. A similar environment in the embedded product segment eliminates the need for retraining of personnel since they are already familiar with the look and feel of the system. Often times, it helps to be able to have little or no difference between the embedded and desktop device from a user interface perspective.

In Windows CE, the PC is used to prototype peripherals and develop device drivers; all development is done on the PC. If the target platform is also Intel Architecture, the large knowledge base for Intel Architecture can be utilized for hardware expertise, programmers, training materials, and sample code. Intel Architecture CISC is very efficient for all Windows operating systems. Since a lot of optimization effort has already been spent on the PC, reuse of PC developments can result in faster time-to-market. This is possible if the architecture of the Windows CE target is the same as the PC. The Windows CE Embedded Toolkit includes PC chipset and peripheral support, including basic VGA drivers and S3 accelerated drivers.

There are some differences between programming for the desktop and programming in Windows CE. Since Windows CE programs are required to have a small memory footprint, an important aspect of its programming is the need to manage with limited memory. Since memory usage must be minimized, having knowledge of memory allocations with Windows CE is important.

Embedded systems may stay powered-on for long periods of time. Programmers need to keep this in mind to ensure that the programs run flawlessly for many months at a time. Modifications must be made to the OEM Adaptation Layer. Since different solutions are possible for different applications, the varying need for applications can be met.