HMS81032TL datasheet(19/77 Pages) HYNIX

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HMS81004E/08E/16E/24E/32E

JUNE 2001 Ver 1.00

8. MEMORY ORGANIZATION

The HMS81004E/08E/16E/24E/32E has separate address

spaces for Program memory and Data Memory. Program

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

32K bytes of Program memory. Data memory can be read

and written to up to 448 bytes including the stack area.

8.1 Registers

This device has six registers that are the Program Counter

(PC), an 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.

Figure 8-1 Configuration of Registers

Accumulator:

The Accumulator is the 8-bit general purpose register, used

for data operation such as transfer, temporary saving, and

conditional judgement, etc. The Accumulator can be used

as a 16-bit register with Y Register as shown below.

In the case of multiplication instruction, execute as a mul-

tiplier register. After multiplication operation, the lower 8-

bit of the result enters. (Y*A => YA). In the case of divi-

sion instruction, execute as the lower 8-bit of dividend. Af-

ter division operation, quotient enters.

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 specified address,

which becomes the actual address. These modes are ex-

tremely effective for referencing subroutine tables and

memory tables. The index registers also have increment,

decrement, comparison and data transfer functions, and

they can be used as simple accumulators.

• X Register

In the case of division instruction, execute as register.

• Y Register

In the case of 16-bit operation instruction, execute as the

upper 8-bit of YA. (16-bit accumulator). In the case of

multiplication instruction, execute as a multiplicand regis-

ter. After multiplication operation, the upper 8-bit of the

result enters. In the case of division instruction, execute as

the upper 8-bit of dividend. After division operation, re-

mains enters. Y register can be used as loop counter of

conditional branch command. (e.g.DBNE Y, rel)

Stack Pointer:

The Stack Pointer is an 8-bit register used for occurrence

interrupts, calling out subroutines and PUSH, POP, RETI,

RET instruction. Stack Pointer identifies the location in the

stack to be accessed (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 SP is post-decremented when a subrou-

tine call or a push instruction is executed, or when an inter-

rupt is accepted. The SP is pre-incremented when a return

or a pop instruction is executed.

The stack can be located at any position within 100H to

1FFH of the internal data memory. The SP is not initialized

by hardware, requiring to write the initial value (the loca-

tion with which the use of the stack starts) by using the ini-

tialization routine. Normally, the initial value of "FFH" is

ACCUMULATOR

X REGISTER

Y REGISTER

STACK POINTER

PROGRAM COUNTER

PROGRAM STATUS

WORD

PCL

PCH

PSW

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

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