
Lesson 3: Boolean Logic
From "The Digital I/O Handbook"
by Jon Titus and Tom Oâ€™Hanlan
Sealevel System, Liberty, SC, 2004
The world of digital electronics allows for only two states, so at a given time, a digital signal can exist
in only one of them. Although engineers usually think of these two binary states as logic 0 and logic 1, you
can define them as you wish: true and false, black and white, high and low, and so on, as long as everyone
else understands your definitions. Basic Boolean logic operations such as AND and OR let electronic circuits
make decisions, such as, "If A and B are true, do this..." Figure 11 shows the AND and OR logic operations
along with the symbol engineers use to represents each operation in a circuit. A truth table shows the output
condition produced for each possible set of inputs to the logic circuit, called a "gate." A 2input gate, for
example, has 22, or 4 possible input conditions, while a 5input gate would allow for 25, or 32 possible binary
input combinations.
Read More: http://www.sealevel.com/knowledgebase/article.asp?article_id=63
From "AMERICAN LABORATORY"
by Peter R. Rony, David G. Larsen, and Jonathan A. Titus
"What Is a Logical Instruction"
MOST MICROCOMPUTERS manipulate information eight bits at a time. For example, the 8080A chip can move
the eight bits from internal register to internal register, from internal register to memory, and between the
accumulator and an external I/O device. It can also perform arithmetic and logical operations, the
former including add, subtract, and compare, and the latter including AND, OR, ExclusiveOR, and complement.
In this column, we shall be concerned with the logical operations.
The basic rules governing onebit logic operations are truth tables. A truth table can be defined as a
tabulation that shows the relation of all output logic levels of a digital circuit
to all possible combinations of input logic levels in such a way as to characterize the circuit functions
completely. I The truth tables for the AND, OR, ExclusiveOR, and complement operations are given in
Table 1. We call these truth tables onebit tables because the data words, A and B, each contain only a
single bit.
Read More: What Is A Logical Instruction.pdf [49.2KB]
