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MICROCOMPUTER INSTRUMENTATION AND CONTROL 4

abbreviations are only for the convenience of the programmer because the
program that the microcomputer eventually runs must be in the form of
binary numbers. When each instruction is converted to the binary code
that the microcomputer recognizes, it is called a machine language
program.
Once the program has The assembly language abbreviation for the jump instruction is JMP.
been written in assembly Table 4.1 shows the assembly language equivalents for typical microcomputer
language, a special kind instructions, along with a detailed description of the operation called for by
of program, called an the instruction. When writing a microcomputer program, it is easier and
assembler, converts the faster to use the abbreviated name rather than the complete function name.
assembly language pro- Assembly language simplifies programming tasks for the computer
gram into the binary programmer because the abbreviations are easier to remember and write than
code recognized by the the binary numbers the computer uses. However, the program eventually
microcomputer. must be converted to the binary codes that the microcomputer recognizes as
instructions, which is done by a special program called an assembler. The
assembler program is run on the computer to convert assembly language to
binary codes. This enables the programmer to write the program using words
that have meaning to the programmer and also to produce machine codes
that the computer can use.

Logic Functions
A microcomputer can Microprocessors are capable of performing all of the basic logic functions
AND the contents of its such as AND, OR, NOT, and combinations of these. For instance, the NOT
accumulator with a operation affects the accumulator by changing all ones to zeros and zeros to
memory location to per- ones. Other logic functions are performed by using the contents of the
form the logical AND accumulator and some memory location. All eight bits of the accumulator are
function. affected, and all are changed at the same time. As shown in Figure 4.13, the
AND operation requires two inputs. One input is the contents of the
accumulator, and the other input is the contents of a memory location; thus,
the eight accumulator bits are ANDed with the eight memory bits. The AND
operation is performed on a bit-by-bit basis. For instance, bit 0 of the
accumulator (the rightmost bit) is ANDed with bit 0 of the memory location,
bit 1 with bit 1, bit 2 with bit 2, and so on. In other words, the AND operation
is performed as if eight AND gates were connected with one input to a bit in
the accumulator, and with the other input to a bit (in the same position) in the
memory location. The resulting AND outputs are stored back into the
accumulator in the corresponding bit positions. The OR logic function is
performed in exactly the same way as the AND except that a 1 would be
produced at the output if signal A or signal B were a 1, or if both were a 1 (i.e.,
using OR logic).

UNDERSTANDING AUTOMOTIVE ELECTRONICS 119