PalmPower scores another exclusive this month with this important article by Motorola engineer Perry Vo. If you ever wondered about the processor inside your PalmPilot (literally the brains of your PalmPilot), now you can find out. Although by nature technical, this article makes understanding the functions of the PalmPilot processor clear to everyone.

Just like in desktop computers, the microprocessor is the brain of handheld devices. It does all the thinking, receives inputs, makes decisions based on the inputs, and produces outputs. Microprocessors nowadays are not only faster and smarter, but also integrate more functionality. This trend enables engineers to design portable handheld products that have as much processing power as a desktop computer.

At the heart of the PalmPilot is the Motorola MC68328 (code named Dragonball), which is a low-cost, low-power, highly integrated microprocessor. Running at 16 MHz clock speed, the MC68328 is optimized to offers four times the performance of the microprocessor in the first Apple Macintosh computer model. Moreover, most of the circuitry in a standard desktop PC has shrunk into a small square package of about 15x15 millimeters, so that what used to occupy half of your desk fits nicely in the palm of your hand.

Inside the MC68238
Figure A shows the internal structure of the processor. The MC68328 microprocessor can directly address up to four gigabytes of external memory. When the processor needs to store or retrieve information at a certain location in a range of memory space, external decoding circuitry is required so that the processor knows which memory device and which location in that memory device it needs to access. In the old days, depending on the memory layout, this decoding circuitry could involve as many as 15 additional electronic components with complex wiring logic. On the MC68328, all memory decoding circuitry is integrated inside the system integration module (SIM).