Glossary
68HC(9)12DG128 Rev 1.0
MOTOROLA
Glossary
419
reserved memory location
— A memory location that is used only in special factory test modes.
Writing to a reserved location has no effect. Reading a reserved location returns an
unpredictable value.
reset
— To force a device to a known condition.
ROM
— Read-only memory. A type of memory that can be read but cannot be changed (written).
The contents of ROM must be specified before manufacturing the MCU.
SCI
— See "serial communication interface module (SCI)."
serial
— Pertaining to sequential transmission over a single line.
serial communications interface module (SCI)
— A module that supports asynchronous
communication.
serial peripheral interface module (SPI)
— A module that supports synchronous
communication.
set
— To change a bit from logic 0 to logic 1; opposite of clear.
shift register
— A chain of circuits that can retain the logic levels (logic 1 or logic 0) written to
them and that can shift the logic levels to the right or left through adjacent circuits in the
chain.
signed
— A binary number notation that accommodates both positive and negative numbers.
The most significant bit is used to indicate whether the number is positive or negative,
normally logic 0 for positive and logic 1 for negative. The other seven bits indicate the
magnitude of the number.
software
— Instructions and data that control the operation of a microcontroller.
software interrupt (SWI)
— An instruction that causes an interrupt and its associated vector
fetch.
SPI
— See "serial peripheral interface module (SPI)."
stack
— A portion of RAM reserved for storage of CPU register contents and subroutine return
addresses.
stack pointer (SP)
— A 16-bit register in the CPU containing the address of the next available
storage location on the stack.
start bit
— A bit that signals the beginning of an asynchronous serial transmission.
status bit
— A register bit that indicates the condition of a device.
stop bit
— A bit that signals the end of an asynchronous serial transmission.