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.
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
The A and B columns represent the A and B inputs. The column is true if the input is high.
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.
The Q column selects the result of the truth table for each possible state of the inputs.
Below the dark header row, the truth table has eight more rows, one for each possible state of the inputs.
In each row, the first three columns represent a possible state of the three inputs.
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.
The Q output emits the result of the truth table for the given inputs. 10V represents true, and 0V represents false.
¬Q: emits the negation of Q.
Beside each output is a button that momentarily sets the output to true and the other output to false.
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.