Glossary
MC68HC908AZ60A — Rev 2.0
Technical Data
MOTOROLA
Glossary
449
illegal address
— An address not within the memory map
illegal opcode
— A nonexistent opcode.
I
— The interrupt mask bit in the condition code register of the CPU08. When I is set, all interrupts
are disabled.
index register (H:X)
— A 16-bit register in the CPU08. The upper byte of H:X is called H. The
lower byte is called X. In the indexed addressing modes, the CPU uses the contents of
H:X to determine the effective address of the operand. H:X can also serve as a temporary
data storage location.
input/output (I/O)
— Input/output interfaces between a computer system and the external world.
A CPU reads an input to sense the level of an external signal and writes to an output to
change the level on an external signal.
instructions
— Operations that a CPU can perform. Instructions are expressed by programmers
as assembly language mnemonics. A CPU interprets an opcode and its associated
operand(s) and instruction.
interrupt
— A temporary break in the sequential execution of a program to respond to signals
from peripheral devices by executing a subroutine.
interrupt request
— A signal from a peripheral to the CPU intended to cause the CPU to
execute a subroutine.
I/O
— See “input/output (I/0).”
IRQ
— See "external interrupt module (IRQ)."
jitter
— Short-term signal instability.
latch
— A circuit that retains the voltage level (logic 1 or logic 0) written to it for as long as power
is applied to the circuit.
latency
— The time lag between instruction completion and data movement.
least significant bit (LSB)
— The rightmost digit of a binary number.
logic 1
— A voltage level approximately equal to the input power voltage (V
DD
).
logic 0
— A voltage level approximately equal to the ground voltage (V
SS
).
low byte
— The least significant eight bits of a word.
low voltage inhibit module (LVI)
— A module in the M68HC08 Family that monitors power
supply voltage.
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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.