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APPENDIX B – GLOSSARY
that the CPU needs.
—M—
MCU – Microcontroller unit
Microcontroller. A complete computer
system including CPU, memory, clock
oscillator, and I/O on a single integrated
circuit.
—N—
N
Abbreviation for negative, a bit in the
condition code register of the
MC68HC908AB32. In
two's-complement computer notation,
positive signed numbers have a 0 in their
MSB (most significant bit) and negative
numbers have a 1 in their MSB. The N
condition code bit reflects the sign of the
result of an operation. After a load
accumulator instruction, the N bit will be
set if the MSB of the loaded value was a
1.
—O—
object code file
A text file containing numbers that
represent the binary opcodes and data of a
computer program. An object code file
can be used to load binary information
into a computer system. Motorola uses
the S-record file format for object code
files.
operand
An input value to a logical or
mathematical operation.
opcode
A binary code that instructs the CPU to do
a specific operation in a specific way. The
B-4
MC68HC908AB32 CPU recognizes 210
unique 8-bit opcodes that represent
addressing mode variations of 62 basic
instructions.
OTPROM
A non-volatile type of memory that can
be programmed but cannot be erased. An
OTPROM is an EPROM MCU that is
packaged in an opaque plastic package. It
is called a one-time-programmable MCU
because there is no way to expose the
EPROM to a UV light.
—P—
PC
Abbreviation for program counter CPU
register of the MC68HC908AB32.
program counter
The CPU register that holds the address
of the next instruction or operand that the
CPU will use.
—Q—
—R—
RAM
Random Access Memory. Any RAM
location can be read or written by the
CPU. The contents of a RAM memory
location remain valid until the CPU
writes a different value or until power is
turned off.
registers
Memory locations that are wired directly
into the CPU logic instead of being part of
the addressable memory map. The CPU
always has direct access to the
information in these registers. The CPU
registers in the MC68HC908AB32 are A
M68ICS08ABUM/D
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