Why does this counter count?

[jimktrains]

I was playing around with trying to design a quadrature decoder. I haven't added a switch to flip the order of the A and B signals in this example, so it should never count Counterclockwise, but it always ends up counting.

I am manually clicking the clock. Here is the first pulse where the CCW counter counts.

Here is the first pulse, to show it's not like that at the start.

Here is the file. (I can't seem to attach it.) quadrature-encoder-example.dig :

<?xml version="1.0" encoding="utf-8"?>
<circuit>
  <version>1</version>
  <attributes/>
  <visualElements>
    <visualElement>
      <elementName>Clock</elementName>
      <elementAttributes>
        <entry>
          <string>rotation</string>
          <rotation rotation="2"/>
        </entry>
      </elementAttributes>
      <pos x="1220" y="80"/>
    </visualElement>
    <visualElement>
      <elementName>Decoder</elementName>
      <elementAttributes>
        <entry>
          <string>Selector Bits</string>
          <int>3</int>
        </entry>
        <entry>
          <string>rotation</string>
          <rotation rotation="2"/>
        </entry>
      </elementAttributes>
      <pos x="1000" y="180"/>
    </visualElement>
    <visualElement>
      <elementName>Counter</elementName>
      <elementAttributes>
        <entry>
          <string>rotation</string>
          <rotation rotation="2"/>
        </entry>
        <entry>
          <string>Bits</string>
          <int>3</int>
        </entry>
      </elementAttributes>
      <pos x="1180" y="100"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>rotation</string>
          <rotation rotation="2"/>
        </entry>
      </elementAttributes>
      <pos x="1200" y="100"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>rotation</string>
          <rotation rotation="2"/>
        </entry>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="1200" y="60"/>
    </visualElement>
    <visualElement>
      <elementName>Or</elementName>
      <elementAttributes>
        <entry>
          <string>rotation</string>
          <rotation rotation="2"/>
        </entry>
        <entry>
          <string>Inputs</string>
          <int>3</int>
        </entry>
      </elementAttributes>
      <pos x="620" y="200"/>
    </visualElement>
    <visualElement>
      <elementName>Or</elementName>
      <elementAttributes>
        <entry>
          <string>rotation</string>
          <rotation rotation="2"/>
        </entry>
        <entry>
          <string>Inputs</string>
          <int>3</int>
        </entry>
      </elementAttributes>
      <pos x="620" y="120"/>
    </visualElement>
    <visualElement>
      <elementName>Seven-Seg-Hex</elementName>
      <elementAttributes/>
      <pos x="1040" y="-120"/>
    </visualElement>
    <visualElement>
      <elementName>Splitter</elementName>
      <elementAttributes>
        <entry>
          <string>mirror</string>
          <boolean>true</boolean>
        </entry>
        <entry>
          <string>rotation</string>
          <rotation rotation="1"/>
        </entry>
        <entry>
          <string>Input Splitting</string>
          <string>3,1</string>
        </entry>
        <entry>
          <string>Output Splitting</string>
          <string>4</string>
        </entry>
      </elementAttributes>
      <pos x="1080" y="60"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="1060" y="80"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="1100" y="40"/>
    </visualElement>
    <visualElement>
      <elementName>Monoflop</elementName>
      <elementAttributes/>
      <pos x="720" y="300"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="700" y="320"/>
    </visualElement>
    <visualElement>
      <elementName>Monoflop</elementName>
      <elementAttributes/>
      <pos x="720" y="380"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="700" y="400"/>
    </visualElement>
    <visualElement>
      <elementName>Not</elementName>
      <elementAttributes/>
      <pos x="600" y="380"/>
    </visualElement>
    <visualElement>
      <elementName>Probe</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>A</string>
        </entry>
      </elementAttributes>
      <pos x="540" y="220"/>
    </visualElement>
    <visualElement>
      <elementName>Probe</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>P</string>
        </entry>
      </elementAttributes>
      <pos x="860" y="340"/>
    </visualElement>
    <visualElement>
      <elementName>Probe</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>N</string>
        </entry>
      </elementAttributes>
      <pos x="820" y="340"/>
    </visualElement>
    <visualElement>
      <elementName>Counter</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>CwCount</string>
        </entry>
        <entry>
          <string>Bits</string>
          <int>4</int>
        </entry>
      </elementAttributes>
      <pos x="1180" y="280"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes/>
      <pos x="1160" y="280"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="1160" y="320"/>
    </visualElement>
    <visualElement>
      <elementName>Seven-Seg-Hex</elementName>
      <elementAttributes/>
      <pos x="1320" y="220"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="1380" y="380"/>
    </visualElement>
    <visualElement>
      <elementName>And</elementName>
      <elementAttributes>
        <entry>
          <string>wideShape</string>
          <boolean>true</boolean>
        </entry>
      </elementAttributes>
      <pos x="900" y="260"/>
    </visualElement>
    <visualElement>
      <elementName>And</elementName>
      <elementAttributes>
        <entry>
          <string>wideShape</string>
          <boolean>true</boolean>
        </entry>
      </elementAttributes>
      <pos x="900" y="380"/>
    </visualElement>
    <visualElement>
      <elementName>Not</elementName>
      <elementAttributes/>
      <pos x="820" y="260"/>
    </visualElement>
    <visualElement>
      <elementName>Or</elementName>
      <elementAttributes>
        <entry>
          <string>wideShape</string>
          <boolean>true</boolean>
        </entry>
      </elementAttributes>
      <pos x="1040" y="280"/>
    </visualElement>
    <visualElement>
      <elementName>Probe</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>B</string>
        </entry>
      </elementAttributes>
      <pos x="540" y="140"/>
    </visualElement>
    <visualElement>
      <elementName>Probe</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>CwClock</string>
        </entry>
      </elementAttributes>
      <pos x="1140" y="220"/>
    </visualElement>
    <visualElement>
      <elementName>Counter</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>CcwCount</string>
        </entry>
        <entry>
          <string>Bits</string>
          <int>4</int>
        </entry>
      </elementAttributes>
      <pos x="1180" y="500"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes/>
      <pos x="1160" y="500"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="1160" y="540"/>
    </visualElement>
    <visualElement>
      <elementName>Seven-Seg-Hex</elementName>
      <elementAttributes/>
      <pos x="1320" y="440"/>
    </visualElement>
    <visualElement>
      <elementName>Const</elementName>
      <elementAttributes>
        <entry>
          <string>Value</string>
          <long>0</long>
        </entry>
      </elementAttributes>
      <pos x="1380" y="600"/>
    </visualElement>
    <visualElement>
      <elementName>And</elementName>
      <elementAttributes>
        <entry>
          <string>wideShape</string>
          <boolean>true</boolean>
        </entry>
      </elementAttributes>
      <pos x="900" y="480"/>
    </visualElement>
    <visualElement>
      <elementName>And</elementName>
      <elementAttributes>
        <entry>
          <string>wideShape</string>
          <boolean>true</boolean>
        </entry>
      </elementAttributes>
      <pos x="900" y="600"/>
    </visualElement>
    <visualElement>
      <elementName>Or</elementName>
      <elementAttributes>
        <entry>
          <string>wideShape</string>
          <boolean>true</boolean>
        </entry>
      </elementAttributes>
      <pos x="1040" y="500"/>
    </visualElement>
    <visualElement>
      <elementName>Probe</elementName>
      <elementAttributes>
        <entry>
          <string>Label</string>
          <string>CcwClock</string>
        </entry>
      </elementAttributes>
      <pos x="1140" y="440"/>
    </visualElement>
  </visualElements>
  <wires>
    <wire>
      <p1 x="620" y="160"/>
      <p2 x="660" y="160"/>
    </wire>
    <wire>
      <p1 x="720" y="160"/>
      <p2 x="960" y="160"/>
    </wire>
    <wire>
      <p1 x="700" y="320"/>
      <p2 x="720" y="320"/>
    </wire>
    <wire>
      <p1 x="1160" y="320"/>
      <p2 x="1180" y="320"/>
    </wire>
    <wire>
      <p1 x="1020" y="320"/>
      <p2 x="1040" y="320"/>
    </wire>
    <wire>
      <p1 x="820" y="480"/>
      <p2 x="900" y="480"/>
    </wire>
    <wire>
      <p1 x="800" y="640"/>
      <p2 x="900" y="640"/>
    </wire>
    <wire>
      <p1 x="1180" y="100"/>
      <p2 x="1200" y="100"/>
    </wire>
    <wire>
      <p1 x="1020" y="100"/>
      <p2 x="1080" y="100"/>
    </wire>
    <wire>
      <p1 x="620" y="100"/>
      <p2 x="960" y="100"/>
    </wire>
    <wire>
      <p1 x="500" y="100"/>
      <p2 x="560" y="100"/>
    </wire>
    <wire>
      <p1 x="1080" y="100"/>
      <p2 x="1120" y="100"/>
    </wire>
    <wire>
      <p1 x="860" y="260"/>
      <p2 x="880" y="260"/>
    </wire>
    <wire>
      <p1 x="500" y="260"/>
      <p2 x="820" y="260"/>
    </wire>
    <wire>
      <p1 x="880" y="260"/>
      <p2 x="900" y="260"/>
    </wire>
    <wire>
      <p1 x="500" y="420"/>
      <p2 x="800" y="420"/>
    </wire>
    <wire>
      <p1 x="800" y="420"/>
      <p2 x="820" y="420"/>
    </wire>
    <wire>
      <p1 x="820" y="420"/>
      <p2 x="900" y="420"/>
    </wire>
    <wire>
      <p1 x="620" y="200"/>
      <p2 x="720" y="200"/>
    </wire>
    <wire>
      <p1 x="1120" y="520"/>
      <p2 x="1140" y="520"/>
    </wire>
    <wire>
      <p1 x="840" y="520"/>
      <p2 x="900" y="520"/>
    </wire>
    <wire>
      <p1 x="1140" y="520"/>
      <p2 x="1180" y="520"/>
    </wire>
    <wire>
      <p1 x="520" y="300"/>
      <p2 x="720" y="300"/>
    </wire>
    <wire>
      <p1 x="1120" y="300"/>
      <p2 x="1140" y="300"/>
    </wire>
    <wire>
      <p1 x="780" y="300"/>
      <p2 x="840" y="300"/>
    </wire>
    <wire>
      <p1 x="1140" y="300"/>
      <p2 x="1180" y="300"/>
    </wire>
    <wire>
      <p1 x="860" y="300"/>
      <p2 x="900" y="300"/>
    </wire>
    <wire>
      <p1 x="840" y="300"/>
      <p2 x="860" y="300"/>
    </wire>
    <wire>
      <p1 x="700" y="140"/>
      <p2 x="960" y="140"/>
    </wire>
    <wire>
      <p1 x="500" y="140"/>
      <p2 x="540" y="140"/>
    </wire>
    <wire>
      <p1 x="980" y="620"/>
      <p2 x="1020" y="620"/>
    </wire>
    <wire>
      <p1 x="1180" y="80"/>
      <p2 x="1220" y="80"/>
    </wire>
    <wire>
      <p1 x="620" y="80"/>
      <p2 x="960" y="80"/>
    </wire>
    <wire>
      <p1 x="700" y="400"/>
      <p2 x="720" y="400"/>
    </wire>
    <wire>
      <p1 x="980" y="400"/>
      <p2 x="1020" y="400"/>
    </wire>
    <wire>
      <p1 x="980" y="20"/>
      <p2 x="1020" y="20"/>
    </wire>
    <wire>
      <p1 x="620" y="180"/>
      <p2 x="700" y="180"/>
    </wire>
    <wire>
      <p1 x="520" y="180"/>
      <p2 x="560" y="180"/>
    </wire>
    <wire>
      <p1 x="1160" y="500"/>
      <p2 x="1180" y="500"/>
    </wire>
    <wire>
      <p1 x="1240" y="500"/>
      <p2 x="1280" y="500"/>
    </wire>
    <wire>
      <p1 x="980" y="500"/>
      <p2 x="1040" y="500"/>
    </wire>
    <wire>
      <p1 x="1160" y="280"/>
      <p2 x="1180" y="280"/>
    </wire>
    <wire>
      <p1 x="1240" y="280"/>
      <p2 x="1280" y="280"/>
    </wire>
    <wire>
      <p1 x="980" y="280"/>
      <p2 x="1040" y="280"/>
    </wire>
    <wire>
      <p1 x="620" y="120"/>
      <p2 x="660" y="120"/>
    </wire>
    <wire>
      <p1 x="660" y="120"/>
      <p2 x="960" y="120"/>
    </wire>
    <wire>
      <p1 x="1280" y="600"/>
      <p2 x="1360" y="600"/>
    </wire>
    <wire>
      <p1 x="880" y="600"/>
      <p2 x="900" y="600"/>
    </wire>
    <wire>
      <p1 x="1280" y="380"/>
      <p2 x="1360" y="380"/>
    </wire>
    <wire>
      <p1 x="640" y="380"/>
      <p2 x="720" y="380"/>
    </wire>
    <wire>
      <p1 x="520" y="380"/>
      <p2 x="600" y="380"/>
    </wire>
    <wire>
      <p1 x="780" y="380"/>
      <p2 x="820" y="380"/>
    </wire>
    <wire>
      <p1 x="820" y="380"/>
      <p2 x="900" y="380"/>
    </wire>
    <wire>
      <p1 x="1180" y="60"/>
      <p2 x="1200" y="60"/>
    </wire>
    <wire>
      <p1 x="520" y="220"/>
      <p2 x="540" y="220"/>
    </wire>
    <wire>
      <p1 x="1160" y="540"/>
      <p2 x="1180" y="540"/>
    </wire>
    <wire>
      <p1 x="1020" y="540"/>
      <p2 x="1040" y="540"/>
    </wire>
    <wire>
      <p1 x="1280" y="280"/>
      <p2 x="1280" y="380"/>
    </wire>
    <wire>
      <p1 x="1280" y="500"/>
      <p2 x="1280" y="600"/>
    </wire>
    <wire>
      <p1 x="800" y="420"/>
      <p2 x="800" y="640"/>
    </wire>
    <wire>
      <p1 x="1060" y="60"/>
      <p2 x="1060" y="80"/>
    </wire>
    <wire>
      <p1 x="1380" y="360"/>
      <p2 x="1380" y="380"/>
    </wire>
    <wire>
      <p1 x="1380" y="580"/>
      <p2 x="1380" y="600"/>
    </wire>
    <wire>
      <p1 x="520" y="180"/>
      <p2 x="520" y="220"/>
    </wire>
    <wire>
      <p1 x="520" y="300"/>
      <p2 x="520" y="380"/>
    </wire>
    <wire>
      <p1 x="520" y="220"/>
      <p2 x="520" y="300"/>
    </wire>
    <wire>
      <p1 x="840" y="300"/>
      <p2 x="840" y="520"/>
    </wire>
    <wire>
      <p1 x="1100" y="20"/>
      <p2 x="1100" y="40"/>
    </wire>
    <wire>
      <p1 x="1360" y="360"/>
      <p2 x="1360" y="380"/>
    </wire>
    <wire>
      <p1 x="1360" y="580"/>
      <p2 x="1360" y="600"/>
    </wire>
    <wire>
      <p1 x="720" y="160"/>
      <p2 x="720" y="200"/>
    </wire>
    <wire>
      <p1 x="880" y="260"/>
      <p2 x="880" y="600"/>
    </wire>
    <wire>
      <p1 x="820" y="340"/>
      <p2 x="820" y="380"/>
    </wire>
    <wire>
      <p1 x="820" y="420"/>
      <p2 x="820" y="480"/>
    </wire>
    <wire>
      <p1 x="660" y="120"/>
      <p2 x="660" y="160"/>
    </wire>
    <wire>
      <p1 x="980" y="20"/>
      <p2 x="980" y="40"/>
    </wire>
    <wire>
      <p1 x="500" y="100"/>
      <p2 x="500" y="140"/>
    </wire>
    <wire>
      <p1 x="500" y="140"/>
      <p2 x="500" y="260"/>
    </wire>
    <wire>
      <p1 x="500" y="260"/>
      <p2 x="500" y="420"/>
    </wire>
    <wire>
      <p1 x="1140" y="220"/>
      <p2 x="1140" y="300"/>
    </wire>
    <wire>
      <p1 x="1140" y="440"/>
      <p2 x="1140" y="520"/>
    </wire>
    <wire>
      <p1 x="1080" y="60"/>
      <p2 x="1080" y="100"/>
    </wire>
    <wire>
      <p1 x="1080" y="20"/>
      <p2 x="1080" y="40"/>
    </wire>
    <wire>
      <p1 x="1020" y="20"/>
      <p2 x="1020" y="100"/>
    </wire>
    <wire>
      <p1 x="1020" y="320"/>
      <p2 x="1020" y="400"/>
    </wire>
    <wire>
      <p1 x="1020" y="540"/>
      <p2 x="1020" y="620"/>
    </wire>
    <wire>
      <p1 x="700" y="140"/>
      <p2 x="700" y="180"/>
    </wire>
    <wire>
      <p1 x="860" y="300"/>
      <p2 x="860" y="340"/>
    </wire>
  </wires>
  <measurementOrdering/>
</circuit>

[jimktrains]

I just realized the AND gate at the very bottom should have been connected to the output of the monoflop. Doing so increments the counter on simulation start. However, I'm still curious why it counted in the configuration in my first post.

Here's the proper configuration.

.
Is there a way to have the measurement graph include the initial state?

[hneemann]

Is there a way to have the measurement graph include the initial state?

Interestingly enough not! I have not noticed that yet. I should possibly change that.

You should not use monoflops. This creates asynchronous signals which are better avoided as they can have all sorts of strange effects. Also, simulating a monoflop is not so easy, because in the simulation it is internally controlled by the clock, which of course is not the case in reality.

But to build a quadrature decoder is actually not so easy. I use this as a lab exercise and the students also have a hard time with it. Especially if they also have to take care of contact bouncing. 😄

In the examples/fsm folder you can find a Moore and a Mealy automaton.