M68HC05 Family — Understanding Small Microcontrollers

Freescale Semiconductor, Inc...
Computer Numbers and Codes
Review
Freescale Semiconductor, Inc.
Computers have two logic levels (0 and 1) so they work in the binary
numbering system. Probably because people have 10 fingers, they work
in the base 10 decimal numbering system.
Hexadecimal numbers use the 16 symbols 0 through 9 and A through F.
Each hexadecimal digit can represent a set of four binary digits exactly.
Table 2 shows the decimal, binary, and hexadecimal equivalents of
various values. A $ symbol is used before a hexadecimal valueor an H
is used after a hexadecimal value to distinguish it from decimal numbers.
ASCII is a widely accepted code that allows alphanumeric information to
be represented as binary values.
Each instruction or variation of an instruction has a unique opcode
(binary value) that the CPU recognizes as a request to perform a specific
instruction. CPUs from different manufacturers have different sets of
opcodes.
Programmers specify instructions by a mnemonic such as INCA. A
computer program, called an assembler, translates mnemonic
instructions into opcodes the CPU can understand.
M68HC05 Family — Understanding Small Microcontrollers — Rev. 2.0
36 Computer Numbers and Codes
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