Motorola M68HC08 Designer Reference Manual page 41

serial communications interface module (SCI) — A module in the M68HC08 Family that
supports asynchronous communication.
serial peripheral interface module (SPI) — A module in the M68HC08 Family 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 CPU08 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.
subroutine — A sequence of instructions to be used more than once in the course of a program.
The last instruction in a subroutine is a return from subroutine (RTS) instruction. At each
place in the main program where the subroutine instructions are needed, a jump or branch
to subroutine (JSR or BSR) instruction is used to call the subroutine. The CPU leaves the
flow of the main program to execute the instructions in the subroutine. When the RTS
instruction is executed, the CPU returns to the main program where it left off.
synchronous — Refers to logic circuits and operations that are synchronized by a common
reference signal.
TIM — See "timer interface module (TIM)."
DRM014 — Rev 0.0
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Designer Reference Manual
41