MC68HC705C9A_1 Datasheet, PDF (43/157 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
General Release Specification
CPU Registers
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.
MC68HC705C9A — Rev. 2.0
Central Processing Unit
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