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--- pfw:clavis [2025-06-14 23:12] – [Background information] mka
+++ pfw:clavis [2025-06-15 08:43] (aktuell) – [Background information] topic of bouncing added mka
@@ Zeile 5: / Zeile 5: @@
 Forth has ''KEY?'' and ''KEY'' to query the computer's keyboard. I therefore call the query of a different individual key something else. Figure below shows such a key.
-{{:pfw:weissertaster.jpg?100|The small white button is on the breadboard at the bottom right of the picture.}}
+{{:pfw:weissertaster.png?100|The small white button is on the breadboard at the bottom right of the picture.}}
@@ Zeile 22: / Zeile 22: @@
    Function:  CONF ( mask -- )
               configure pin as input
-   Function:  CLAVIS? ( -- f )  \ flag f is true or false
+   Function:  CLAVIS? ( mask -- f )  \ flag f is true or false
               check for falling edge at pin
@@ Zeile 28: / Zeile 28: @@
 ==== Forth implementation (noForth) ====
-The port pins are configured using registers. (see Manual)
+The port pins are configured using registers.
 The configuration register table is specified in the code.
 The interrupt register indicates whether a falling edge was present.
@@ Zeile 34: / Zeile 34: @@
 In the direction register, P1.7 is set to digital IN.
 The integrated pull-up resistor is activated to support the high level.
-The integrated Schmidt trigger is set to the falling edge.
+The integrated Schmitt-Trigger Input is set to the falling edge.
 However, no interrupt should occur, so it is disabled.
 The pin is used in the I/O function.
@@ Zeile 118: / Zeile 118: @@
 === What is a Port? ===
+In short: The "port" is formed by 9 registers. The registers are 8 bits wide. Each bit operates on "its" pin. In its basic function, the pin can be used as a digital I/O. The direction register determines whether it is an input or output pin. The interrupt flag register is used here. It can detect a voltage edge and store it as an event bit. The functions of the other registers are described in more detail in the User’s Guide.
 See: Texas Instruments MSP430F2xx, MSP430G2xx Family User’s Guide - 8 Digital I/O, p.339ff
-In short: The "port" is formed by 9 registers. The registers are 8 bits wide. Each bit operates on "its" pin. In its basic function, the pin can be used as a digital I/O. The direction register determines whether it is an input or output. The interrupt flag register is used here. It can detect a voltage edge and store it as an event bit. The functions of the other registers are described in more detail in the User’s Guide.
+=== How long is a key press? ===
+A manual short key press took around 120ms if I tapped the key only once.
+{{:pfw:dauer_kurzer_tastendruck_2025-06-14_18-53-38.png?400|Keystroke registered with the logic analyzer}}
+As you can see in the image, the key //bounces// briefly at the beginning until a stable LOW state is reached.
+{{:pfw:prellen-kurzer_tastendruck_zoom_2025-06-14_18-55-44.png?400|Contact bounces after pressing the button}}
+In the second image, the bounce phase has been enlarged. After about 1ms, the bouncing was over.
+The port pin reacts to the first falling edge. Subsequent edges, caused by bouncing, do not trigger anything. The next falling edge would only be registered once the interrupt flag has been reset by the program.
+More on the [[pfw:topicofbouncing|topic of bouncing]].