M68ICS08KX datasheet(65/77 Pages) MOTOROLA

65 / 77 page

User’s Manual

M68ICS08KX In-Circuit Simulator

Glossary

MOTOROLA

Glossary

C — An abbreviation for carry/borrow in the condition codes register of the

MC68HC908KX8. 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 MC68HC908KX8.

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

bits), SP (stack pointer), and PC (program counter).

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