HC705C9AGRSSLASHD datasheet(43/157 Pages) NXP

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General Release Specification

CPU Registers

MC68HC705C9A — Rev. 2.0

Central Processing Unit

3.3.1 Accumulator (A)

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

operands and results of arithmetic calculations or data manipulations.

3.3.2 Index Register (X)

The index register 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.

3.3.3 Program Counter (PC)

The program counter is a 16-bit register that contains the address of the

next byte to be fetched.

3.3.4 Stack Pointer (SP)

The stack pointer contains the address of the next free location on the

stack. During an MCU reset or the reset stack pointer (RSP) instruction,

the stack pointer is set to location $0FF. The stack pointer is then

decremented as data is pushed onto the stack and incremented as data

is pulled from the stack.

When accessing memory, the eight most significant bits are permanently

set to 00000011. These eight bits are appended to the six least

significant register bits to produce an address within the range of $00FF

to $00C0. Subroutines and interrupts may use up to 64 (decimal)

locations. If 64 locations are exceeded, the stack pointer wraps around

and loses the previously stored information. A subroutine call occupies

two locations on the stack; an interrupt uses five locations.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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