2 A SIMPLE SMART SENSOR

In its basic form, the application features the minimum data treatment: a subtraction is

performed between an entered analog value and a constant reference to control an output

signal generator. This last circuit drives two external I/O pins according to the subtraction

result: Whether the value

is positive or negative, only one of the two outputs is activated

issuing a squarewave signal with a frequency function of the amplitude of the difference.

2.1 Graphical description

The core of this development methodology is the graphical description of the application. This

description uses a standard library allowing a system oriented description; Included are:

Input / Output symbols

Logic / Arithmetic symbols

Oscillators / Pulse generators

State machine for sequencing

With such a library, it is possible to cover most application requirements as long as the time

resolution require for the oscillators and pulse generators remains over 10ms, the value used

as the time unit. This value defines only the minimum calibrated timebase available and not the

speed of the application which is fixed by the MCU quartz crystal frequency and the complexity

of the application.

The graphical description follows a decomposition of the application into such basic

functionalities; In the present case our needs are for:

One analog input with an A/D convertor

One constant reference

One subtraction operator

One wave generator

Two output pins

No sequencing is required.

The analog input and digital outputs are described by placing the appropriate symbols

proposed in the main library of the object menu. The software proposes the MCU I/O pin

available in each case:

digital or analog inputs, current sink capabilities for output pins,

insuring a full compatibility with the selected hardware (Figure 1).

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