MC908AS60ACFU Datasheet, PDF (409/414 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Glossary
mask option register (MOR) — An EPROM location containing bits that enable or disable certain MCU
features.
MCU — Microcontroller unit. See “microcontroller.”
memory location — Each M68HC08 memory location holds one byte of data and has a unique address.
To store information in a memory location, the CPU places the address of the location on the address
bus, the data information on the data bus, and asserts the write signal. To read information from a
memory location, the CPU places the address of the location on the address bus and asserts the read
signal. In response to the read signal, the selected memory location places its data onto the data bus.
memory map — A pictorial representation of all memory locations in a computer system.
microcontroller — Microcontroller unit (MCU). A complete computer system, including a CPU, memory,
a clock oscillator, and input/output (I/O) on a single integrated circuit.
modulo counter — A counter that can be programmed to count to any number from zero to its maximum
possible modulus.
monitor ROM — A section of ROM that can execute commands from a host computer for testing
purposes.
MOR — See "mask option register (MOR)."
most significant bit (MSB) — The leftmost digit of a binary number.
multiplexer — A device that can select one of a number of inputs and pass the logic level of that input
on to the output.
N — The negative bit in the condition code register of the CPU08. The CPU sets the negative bit when
an arithmetic operation, logical operation, or data manipulation produces a negative result.
nibble — A set of four bits (half of a byte).
object code — The output from an assembler or compiler that is itself executable machine code, or is
suitable for processing to produce executable machine code.
opcode — A binary code that instructs the CPU to perform an operation.
open-drain — An output that has no pullup transistor. An external pullup device can be connected to the
power supply to provide the logic 1 output voltage.
operand — Data on which an operation is performed. Usually a statement consists of an operator and
an operand. For example, the operator may be an add instruction, and the operand may be the
quantity to be added.
oscillator — A circuit that produces a constant frequency square wave that is used by the computer as
a timing and sequencing reference.
OTPROM — One-time programmable read-only memory. A nonvolatile type of memory that cannot be
reprogrammed.
overflow — A quantity that is too large to be contained in one byte or one word.
page zero — The first 256 bytes of memory (addresses $0000–$00FF).
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
Freescale Semiconductor
409