MC68HC05L16 Datasheet, PDF (36/146 Pages) Freescale Semiconductor, Inc – Microcontrollers

Central Processor Unit (CPU)
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.
7
0
A
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 may also be used as a temporary storage area.
7
0
X
3.5 Condition Code Register
The condition code register (CCR) is a 5-bit register in which the H, N, Z, and C bits are used to indicate
the results of the instruction just executed, and the I bit is used to enable or disable interrupts. 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.
CCR
H I NZC
Half Carry (H)
This bit is set during ADD and ADC operations to indicate that a carry occurred between bits 3 and 4.
Interrupt (I)
When this bit is set, the timer and external interrupt are masked (disabled). If an interrupt occurs while
this bit is set, the interrupt is latched and processed as soon as the I bit is cleared.
Negative (N)
When set, this bit indicates that the result of the last arithmetic, logical, or data manipulation was
negative.
Zero (Z)
When set, this bit indicates that the result of the last arithmetic, logical, or data manipulation was zero.
Carry/Borrow (C)
When set, this bit indicates that a carry or borrow out of the arithmetic logical unit (ALU) occurred
during the last arithmetic operation. This bit is affected also during bit test and branch instructions and
during shifts and rotates.
MC68HC05L16 • MC68HC705L16 Data Sheet, Rev. 4.1
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Freescale Semiconductor