MC81F4x16
9. MEMORY ORGANIZATION
This MCU has separated address spaces for the *program memory* and the *data Memory*.
The program memory is a ROM which stores a program code. It is not possible to write a data at the
program memory while the MCU is running.
The Data Memory is a REM which is used by MCU at running time.
9.1 Registers
There are few registers which are used for MCU operating.
A
X
ACCUMULATOR
X REGISTER
Y
Y REGISTER
SP
PCL
PSW
STACK POINTER
PROGRAM COUNTER
PROGRAM STATUS WORD
PCH
Figure 9-1 Configuration of Registers
Accumulator( A Register ) : Accumulator is the 8-bit general purpose register, which is used for
accumulating and some data operations such as transfer, temporary saving, and conditional
judgment , etc.
And it can be used as a part of 16-bit register with Y Register as shown below.
Y
Y
A
A
Two 8-bit Registers can be used as a “YA” 16-bit Register
Figure 9-2 Configuration of YA 16-bit Registers
X, Y Registers: In the addressing mode, these are used as a index register. It makes it possible to
access at Xth or Yth memory from specific address. It is extremely effective for referencing a
subroutine table and a memory table.
These registers also have increment, decrement, comparison and data transfer functions, and they
can be used as a simple accumulator.
October 19, 2009 Ver.1.35
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