*********************
Exercises
*********************

.. note::

    We mean by function either FC or FB. Remember that an ``FC`` is a function without memory, it have only ``temporary`` variables.
    An ``FB`` is a function with memory, it have ``static`` variables.

Line equation
==============
Analog signal need to be scaled to a physical unit in order to be understood. Usually analog sensors and actuators are modeled as linear systems.
Write a function that map the value of an analog signal to a physical one (or from physical signal to analog one).
For example, to map voltage to temperature, or to map current to pressure value, or to map a speed to voltage.


Rising edge
=============
Write a function the detect the transition of a signal from 0 to 1. This function have the same functioning of the standard one ``R_TRIG``.


Falling Edge
=============
Write a function the detect the transition of a signal from 1 to 0. This function have the same functioning of the standard one ``F_TRIG``.

Retentive TON
==============
Write a function that count the time if a signal is 1. If the signal go to zero the function should stop counting. If the signal return to one, the function should continue to count from the previous value. Refer to the following timing diagram.

.. figure:: images/tonr.png
    :align: center
    :figwidth: 400px

Blink
=======
Write a function that toggle an output, with a determined frequency. The duty cycle of the signal can be tuned.
Remember the duty cycle is the time (or percentage) of the time when the signal is high. In this exercise use time not percentage.

.. figure:: images/blink.png
    :align: center
    :figwidth: 400px

    Preset times tHigh (on) and tLow (off) can be set as desired

Bi-stable cylinder
=====================

Write a function that control a cylinder. Imagine all digital input and outputs that are necessary to the correct functioning of the cylinder, as also any other signal or variable (not only physical input or output).

.. _figCylDouble:
.. figure:: images/cyl_double.png
    :align: center
    :figwidth: 400px

    Double acting cylinder