allows an input shape to avoid the active low state; see #177

src/main/java/de/neemann/digital/core/element/Keys.java

@@ -395,6 +395,15 @@ public final class Keys {
     public static final Key<Boolean> IS_HIGH_Z
             = new Key<>("isHighZ", false).allowGroupEdit().setSecondary();
 
+    /**
+     * flag to avoid active low at an input
+     */
+    public static final Key<Boolean> AVOID_ACTIVE_LOW
+            = new Key<>("avoidActiveLow", false)
+            .setDependsOn(IS_HIGH_Z)
+            .allowGroupEdit()
+            .setSecondary();
+
     /**
      * the description of an element
      */

src/main/java/de/neemann/digital/core/io/In.java

@@ -35,6 +35,7 @@ public class In implements Element {
             .addAttribute(Keys.LABEL)
             .addAttribute(Keys.INPUT_DEFAULT)
             .addAttribute(Keys.IS_HIGH_Z)
+            .addAttribute(Keys.AVOID_ACTIVE_LOW)
             .addAttribute(Keys.DESCRIPTION)
             .addAttribute(Keys.INT_FORMAT)
             .addAttribute(Keys.PINNUMBER);

src/main/java/de/neemann/digital/draw/shapes/InputShape.java

@@ -32,11 +32,12 @@ public class InputShape implements Shape {
     private final String label;
     private final PinDescriptions outputs;
     private final IntFormat format;
+    private final boolean isHighZ;
+    private final boolean avoidLow;
     private IOState ioState;
     private SingleValueDialog dialog;
     private Value value;
     private Value inValue;
-    private final boolean isHighZ;
 
     /**
      * Creates a new instance
@@ -56,6 +57,8 @@ public class InputShape implements Shape {
         format = attr.get(Keys.INT_FORMAT);
 
         isHighZ = attr.get(Keys.INPUT_DEFAULT).isHighZ() || attr.get(Keys.IS_HIGH_Z);
+
+        avoidLow = isHighZ && attr.get(Keys.AVOID_ACTIVE_LOW);
     }
 
     @Override
@@ -74,8 +77,12 @@ public class InputShape implements Shape {
                 if (value.getBits() == 1) {
                     modelSync.access(() -> {
                         if (isHighZ) {
-                            if (value.isHighZ()) value.setValue(0);
+                            if (value.isHighZ()) {
-                            else if (value.getValue() == 0) value.setValue(1);
+                                if (avoidLow)
+                                    value.setValue(1);
+                                else
+                                    value.setValue(0);
+                            } else if (value.getValue() == 0) value.setValue(1);
                             else value.setToHighZ();
                         } else
                             value.setValue(1 - value.getValue());

src/main/resources/lang/lang_de.xml

@@ -993,6 +993,9 @@ Sind evtl. die Namen der Variablen nicht eindeutig?</string>
     <string name="key_isHighZ">Eingang kann hochohmig sein</string><!-- In, Splitter -->
     <string name="key_isHighZ_tt">Wenn gesetzt, ist ein hochohmiger Eingang erlaubt. Bei einem Eingangselement ist ein
         hochohmiger Eingang auch erlaubt, wenn der Vorgabewert auf hochohmig ("Z") gesetzt wird.</string>
+    <string name="key_avoidActiveLow">Keine Ausgabe von Null.</string>
+    <string name="key_avoidActiveLow_tt">Vermeidet die Ausgabe von Null. Ist vor allem beim Aufbau von Relaisschaltungen
+        hilfreich. Kann nur aktiviert werden, wenn ein hochohmiger Ausgang erlaubt ist.</string>
     <string name="key_Description">Beschreibung</string><!-- Out, In, Text -->
     <string name="key_Description_tt">Eine kurze Beschreibung des Elementes.</string>
     <string name="key_Frequency">Frequenz/Hz</string><!-- Clock -->

src/main/resources/lang/lang_en.xml

@@ -988,6 +988,9 @@
     <string name="key_isHighZ">Is three-state input</string><!-- In, Splitter -->
     <string name="key_isHighZ_tt">If set the input is allowed to be in high-z state. At the input component this is
         also allowed if high-z ("Z") is set as the default value.</string>
+    <string name="key_avoidActiveLow">No zero output.</string>
+    <string name="key_avoidActiveLow_tt">Avoids zero output. This is especially helpful when setting up relay circuits.
+        Can only be activated if a high-z output is allowed.</string>
     <string name="key_Description">Description</string><!-- Out, In, Text -->
     <string name="key_Description_tt">A short description of this element and its usage.</string>
     <string name="key_Frequency">Frequency/Hz</string><!-- Clock -->