MC68HC705MC4MP datasheet(36/180 Pages) FREESCALE

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Central Processing Unit

MC68HC705MC4 — Rev. 2.0

Central Processing Unit

3.3 Accumulator

The accumulator (A) is a general-purpose 8-bit register used to hold

operands and results of arithmetic calculations or data manipulations.

3.4 Index Register

The index register (X) is an 8-bit register used for the indexed

addressing value to create an effective address. The index register also

may be used as a temporary storage area.

3.5 Condition Code Register

The condition code register (CCR) is a 5-bit register in which four bits are

used to indicate the results of the instruction just executed, and the fifth

bit indicates whether interrupts are masked. These bits can be tested

individually by a program, and specific actions can be taken as a result

of their state. Each bit is explained in the following paragraphs.

H — Half Carry

This bit is set during ADD and ADC operations to indicate that a carry

occurred between bits 3 and 4.

I — Interrupt

When this bit is set, timer and external interrupts are masked

(disabled). If an interrupt occurs while this bit is set, the interrupt is

latched and processed as soon as the interrupt bit is cleared.

CCR

HIN

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MC68HC705MC4MP Datasheet(PDF) 36 Page - Freescale Semiconductor, Inc