Page 20 - Embedded Microprocessor Systems Real World Design

product or for special versions? Any of these requirements makes a micro-
processor attractive due to the flexibility of implementing functionality in
firmware.
Fortunately, the job of the system designer is becoming easier. Microprocessor
costs are coming down as speed and performance rise. Even simple microproces-
sors are capable of handling tasks that were limited to dedicated hardware just a
few years ago. When you include very fast processors (such as low-cost DSPs) , the
range of potential applications that can be performed with a microprocessor is
wider than ever.

Processor Selection

Suppose you decide to use a microprocessor for your new widget. What steps do
you take to select the processor to be used? Fortunately, for all but a very few appli-
cations, more than one right solution is possible because several microprocessors
can meet the requirements. As with most real-world engineering decisions, the
selection consists of a series of tradeoffs between cost and functionality. The spe-
cific selection process will depend on the complexity of the finished product, but
the following items must be taken into consideration:

Number of 1/0 pins required
Interfaces required
Memory requirements
Number of interrupts required
Real-time considerations
Development environment
Processing speed required
ROMability
Memory architecture
Power requirements
Environmental requirements
Life cycle costs
Operator training/competence
The “real” requirements

Number of UO Pins
In a minimumcost system, component count is a major factor in the final product
cost. These systems generally use a singlechip microprocessor with internal
ROM and RAM. There is a convention to identify these parts as microcontrollers, to

System Design 5