HMS87C1304A Datasheet, PDF(17/70 Page) Hynix Semiconductor – CMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

HMS87C1304A Datasheet, PDF (17/70 Pages) Hynix Semiconductor – CMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

◁

HYUNDAI MicroElectronics

HMS87C1304A/HMS87C1302A

8. MEMORY ORGANIZATION

The HMS87C1304A and HMS87C1302A have separate

address spaces for Program memory and Data Memory.

Program memory can only be read, not written to. It can be

up to 4K /8K bytes of Program memory. Data memory can

be read and written to up to 192 bytes including the stack

area.

8.1 Registers

This device has six registers that are the Program Counter

(PC), a Accumulator (A), two index registers (X, Y), the

Stack Pointer (SP), and the Program Status Word (PSW).

The Program Counter consists of 16-bit register.

Generally, SP is automatically updated when a subroutine

call is executed or an interrupt is accepted. However, if it

is used in excess of the stack area permitted by the data

memory allocating configuration, the user-processed data

may be lost.

ACCUMULATOR

The stack can be located at any position within 00H to 7FH

X REGISTER

of the internal data memory. The SP is not initialized by

hardware, requiring to write the initial value (the location

Y REGISTER

with which the use of the stack starts) by using the initial-

STACK POINTER

ization routine. Normally, the initial value of â7FHâ is

y PCH

PCL

PSW

PROGRAM COUNTER

PROGRAM STATUS

WORD

ar Figure 8-1 Configuration of Registers

in Accumulator: The Accumulator is the 8-bit general pur-

pose register, used for data operation such as transfer, tem-

lim porary saving, and conditional judgement, etc.

The Accumulator can be used as a 16-bit register with Y

Pre Y

used.

Stack Address (000H ~ 07FH)

Hardware fixed

Note: The Stack Pointer must be initialized by software be-

cause its value is undefined after RESET.

Example: To initialize the SP

LDX

#07FH

TXSP

; SP â 7FH

Program Counter: The Program Counter is a 16-bit wide

which consists of two 8-bit registers, PCH and PCL. This

counter indicates the address of the next instruction to be

executed. In reset state, the program counter has reset rou-

Two 8-bit Registers can be used as a âYAâ 16-bit Register

tine address (PCH:0FFH, PCL:0FEH).

Figure 8-2 Configuration of YA 16-bit Register

X, Y Registers: In the addressing mode which uses these

index registers, the register contents are added to the spec-

ified address, which becomes the actual address. These

modes are extremely effective for referencing subroutine

tables and memory tables. The index registers also have in-

crement, decrement, comparison and data transfer func-

tions, and they can be used as simple accumulators.

Stack Pointer: The Stack Pointer is an 8-bit register used

for occurrence interrupts and calling out subroutines. Stack

Pointer identifies the location in the stack to be accessed

(save or restore).

Program Status Word: The Program Status Word (PSW)

contains several bits that reflect the current state of the

CPU. The PSW is described in Figure 8-3 . It contains the

Negative flag, the Overflow flag, the Break flag the Half

Carry (for BCD operation), the Interrupt enable flag, the

Zero flag, and the Carry flag.

[Carry flag C]

This flag stores any carry or borrow from the ALU of CPU

after an arithmetic operation and is also changed by the

Shift Instruction or Rotate Instruction.

[Zero flag Z]

This flag is set when the result of an arithmetic operation

or data transfer is â0â and is cleared by any other result.

Jan. 2001

Preliminary

▷