Central Processor Unit

 

 

7

 

0

STACK

 

 

 

1

1

1

CONDITION CODE REGISTER

I

 

 

 

 

 

 

 

 

 

R

 

 

 

 

N

 

 

 

 

 

 

 

 

 

 

 

 

 

ACCUMULATOR

T

 

 

 

 

E

 

 

 

 

INCREASING

 

 

 

 

E

 

DECREASING

T

 

 

 

 

 

MEMORY

 

 

INDEX REGISTER

R

 

MEMORY

U

 

 

 

ADDRESSES

R

 

 

 

 

R

 

ADDRESSES

 

 

 

 

 

 

U

 

 

 

 

N

 

 

 

PCH

 

 

 

 

 

 

 

P

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PCL

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UNSTACK

 

 

 

 

 

 

NOTE:

Since the stack pointer decrements during pushes, the PCL is stacked first,

 

followed by PCH, etc. Pulling from the stack is in the reverse order.

 

Figure 3-2. Stacking Order

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 also may be used as a temporary storage area.

7

0

X

General Release Specification

 

MC68HC05RC16 — Rev. 3.0

 

 

 

34

Central Processor Unit

MOTOROLA