Motorola M68LC302CAF20VCT User Manual page 78

Glossary
User's Manual
78
C — An abbreviation for carry/borrow in the condition codes register of the
MC68HC908RK2. When adding two unsigned 8-bit numbers, the C bit
is set if the result is greater than 255 ($FF).
CCR — An abbreviation for condition code register in the MC68HC908RK2.
The CCR has five bits (H, I, N, Z, and C) that can be used to control
conditional branch instructions. The values of the bits in the CCR are
determined by the results of previous operations. For example, after a
load accumulator (LDA) instruction, Z will be set if the loaded value
was $00.
clock — A square wave signal that is used to sequence events in a computer.
command set — The command set of a CPU is the set of all operations that
the CPU knows how to perform. One way to represent an instruction set
is with a set of shorthand mnemonics such as LDA meaning load A.
Another representation of an instruction set is the opcodes that are
recognized by the CPU.
condition codes register — The CCR has five bits (H, I, N, Z, and C) that can
be used to control conditional branch commands. The values of the bits
in the CCR are determined by the results of previous operations. For
example, after a load accumulator (LDA) instruction, Z will be set if
the loaded value was $00.
CPU — Central processor unit. The part of a computer that controls execution
of instructions.
CPU cycles — A CPU clock cycle is one period of the internal bus-rate clock.
Normally, this clock is derived by dividing a crystal oscillator source by
two or more so the high and low times will be equal. The length of time
required to execute an instruction is measured in CPU clock cycles.
CPU 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 an MC68HC908 are A (8-bit accumulator), X (8-bit index
register), CCR (condition code register containing the H, I, N, Z, and C
bits), SP (stack pointer), and PC (program counter).
cycles — See CPU cycles.
Glossary
M68ICS08RK In-Circuit Simulator — Rev. 1.0
MOTOROLA