DESCRIBE THE ELECTRONIC PARAMETERS OF LOGIC
Describe and identify logic symbols and positive and negative logic.
Given the description of positive and negative logics, and the use of symbols.
Demonstrate competency of the task skills and knowledge by correctly responding to 80 percent of the
multiple-choice test questions covering the information given in this lesson.
Learning Event 1:
IDENTIFY THE USE OF POSITIVE AND NEGATIVE LOGIC CIRCUITS
Symbols are used to present basic binary circuits because the symbols are time savers. Each
logic symbol represents an entire circuit. By using the symbols, large schematics of electronic
equipment can be reduced to smaller prints called logic diagrams. You no longer have to trace a signal
through a complicated schematic if a logic diagram is available. Logic diagrams are more concise and
easier to read and understand.
For example, suppose that after studying the circuit shown in Figure 1-1 you find that it has a set
pattern of operation. Each time you press two buttons the circuit operates and the bell rings. Once you
have studied the schematic and learned how the circuit rings the bell, there is no need to trace through
the entire schematic each time the two buttons are pressed. You know why the bell rings; now you need
to know when it rings.
a. Replacing the entire schematic with one symbol, as shown in Figure 1-2, you can then say,
"If you know the inputs, you can predict the output." Each time you see that symbol you will recognize
it as a bell-ringer circuit and, logically, closing two input switches will ring the bell.