Exercises with rising / falling
edge detection
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Last updated:
24-09-12 |
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A program formed by Control
Structures - which enables the computer to perform decisions and
loops (that's all it takes)
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The purpose of the exercises below
will be to introduce some of the control structures and how they can implement
the wanted functionality of a program.
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01_Counters_v1: The if statement
and if .. else statement
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if ( condition)
statement1; |
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if ( condition)
statement1;
else statement2;
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Hints / answers |
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| Without the else
statement - both if statements detected
in the while loop
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| With the else
statement - the second if statement only
detected if SENSOR_1 not being pressed
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01_Counters_v2:
The
order of statements - if ... while
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A
program executed in a sekventiel
manner -- Your Sensor press
(SENSOR_1==1) comes randomly in the
excution. |
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In
many programs do you want to detect
when a signal changes from
0 to
1 (Rising
edge) |
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In
the PLC world will a "one shot" do
the trick of
0 =>
1 or
1 =>
0
detection.
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01_Counters_v3:
Detection of rising and falling edges (shift
0->1
and 1->0)
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Hints / answers |
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| The bad thing about
this solution, will be the fact that the
program will "wait forever" in the while
loops doing nothing but waiting. (waste
of time) |
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No matter which platform (PC, PLC,
Microcontroller) you want to write a program for, will
you have to deal with detection of edges /changes of
signals.
In the PLC world will you be able to use ONE-SHOTS, but
its easy to create your own edge detection.
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01_Counters_v4:
"Open wait loops" - "Run To Complete" -
Boolean operators
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If a
variable got the value 0 will it be
FALSE (Boolean value) |
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If a
variable got a value different then
0 will it be TRUE (Boolean value)
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The
statement
old1==0 will be the
same as !old1
- Note
! operator =
Boolean NOT |
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The
statement
new1!=0 will be the
same as new1 -
Hence
!old1 && new1 will be
TRUE when old1=FALSE and new1=TRUE
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Instead of using
while (condition == TRUE) do nothing but wait loop;
will it be better to use "open wait loops"
which also called - "run to complete programming". |
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Hints / answers |
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&& = Boolean and
& = Bitwise and
| | = Boolean or
| = Bitwise or
$$ = Boolean xor
$ = Bitwise xor
! = Boolean not
~ = Bitwise not
Example A=5 (01012)
B=12 (11002) C=0
A && B = 1 as TRUE and TRUE = TRUE
A & B = 4 (01002)
A | | B = 1 as
TRUE or TRUE = TRUE
A | B = 13 (11012)
!A = 0 as not TRUE = FALSE
!C = 1 as not FALSE = TRUE
~A = 1111 1111 1111 1010 2 =
-6 (or 65530) |
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01_Counters_v5:
"Run to complete" version 2 -
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01_Counters_v6:
"Run to complete" version 3 - with
debouncing (prelfang)
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