The Truth Modules
Customizable truth tables with 2, 3, or 4 inputs.
Truth 3 is shown, and described below. Truth 2 and Truth 4 offer similar functionality, with 2 and 4 inputs, respectively.
Controls
Inputs
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A, B, and C/GATE: The input signals for the truth table. A voltage above 0.5V (half a volt) is considered high. A voltage of 0.5V or below is considered low.
Beside each input is an override button that sets the input signal high while pressed.
The Truth Table
Columns
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The A and B columns represent the A and B inputs. The column is true if the input is high.
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The third column represents the condition of the C/GATE input. The button at the top of the column selects a condition to apply to the C/GATE signal. When the signal satisfies the condition, the column is true.
The conditions are:
- HIGH: The gate is high.
- LOW: The gate is low.
- RISE: The gate rises.
- FALL: The gate falls.
- EDGE: The gate changes (rises or falls).
See Usage Notes for ideas about how to use the conditions.
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The Q column selects the result of the truth table for each possible state of the inputs.
Rows
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Below the dark header row, the truth table has eight more rows, one for each possible state of the inputs.
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In each row, the first three columns represent a possible state of the three inputs.
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The button in the Q column selects the result of the truth table when the inputs match the row’s state. The possible results are:
- T: Emit 10V.
- F: Emit 0V.
- Q: Leave the output unchanged.
- ¬Q: Toggle the output.
Outputs
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The Q output emits the result of the truth table for the given inputs. 10V represents true, and 0V represents false.
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¬Q: emits the negation of Q.
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Beside each output is a button that momentarily sets the output to true and the other output to false.
Usage Notes
Level-Triggered vs Edge-Triggered
Level-Sensitive. The HIGH and LOW conditions make the table sensitive to the level of the C/GATE input. This makes the C/GATE input useful as an enable signal, such as for a D Latch.
Edge-Triggered. The RISE, FALL, and EDGE conditions make the table edge-triggered. This makes the C/GATE input useful as a clock signal, allowing changes only at precise moments, when the clock rises or falls.
Note that RISE, FALL, and EDGE are single sample events.
Caution: Selecting the ¬Q Result
Because the ¬Q result causes the table’s output to toggle, it tends to be useful only for edge-triggered rows. That is, only when:
- The C/GATE button selects an edge-triggered condition (RISE, FALL, or EDGE).
- The row’s value for the gate column is T.
To see why, consider: If the row is level-triggered, it might be selected for many samples in a row. On each sample, the output toggles, producing a square wave at the Nyquist frequency. That’s probably not what you want.