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HMS81C4316

CMOS SINGLE-CHIP 8-BIT MICROCONTROLLER FOR TELEVISION

Hynix Semiconductor 

HMS81C43xx / GMS87C4060

8. MEMORY ORGANIZATION

The GMS81C43xx/GMS87C4060 has separate address

spaces for Program memory, Data Memory and Display

memory. Program memory can only be read, not written

to. It can be up to 32K/60K bytes of Program memory.

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.

PCH

A

X

Y

SP

PCL

PSW

ACCUMULATOR

X REGISTER

Y REGISTER

STACK POINTER

PROGRAM COUNTER

PROGRAM STATUS

WORD

Figure 8-1 Configuration of Registers

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

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

porary saving, and conditional judgement, etc.

The Accumulator can be used as a 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 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

Data memory can be read and written to up to 256~512/

1,536 bytes including the stack area. Font memory has pre-

pared 16K bytes for OSD.

(save or restore).

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.

The stack can be located at any position within 0100H to

01FFH of the internal data memory. The SP is not initial-

ized by hardware, requiring to write the initial value (the

location with which the use of the stack starts) by using the

initialization routine. Normally, the initial value of "FFH"

is used.

Stack Address ( 0100H ~ 013F or 01FFH )

15

87

0

01

SP

Hardware fixed

Caution:

The Stack Pointer must be initialized by software be-

cause its value is undefined after RESET.

Example: To initialize the SP for 81C4324 (256 RAM)

LDX #03FH

TXSP

; SP ← 3FH

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-

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

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

18

N ovem ber 2001 ver 1.2

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