HT83R074 datasheet(9/38 Pages) HOLTEK

9 / 38 page

HT83R074

Rev. 1.00

May 17, 2007

Program Memory

- ROM

The program memory stores the program instructions

that are to be executed. It also includes data, table and

interrupt entries, addressed by the program counter

along with the table pointer. The program memory size

for HT83R074 is 2048

´15 bits. Certain locations in the

program memory are reserved for special usage:

· Location 000H

This area is reserved for program initialization. The

program always begins execution at location 000H

each time the system is reset.

· Location 004H

This area is reserved for the time base interrupt ser-

vice program. If the ETBI (intc.1) is activated, and the

interrupt is enabled and the stack is not full, the pro-

gram will jump to location 004H and begins execution.

· Location 008H

This area is reserved for the 8-bit Timer Counter 0 in-

terrupt service program. If a timer interrupt results

from a Timer Counter 0 overflow, and if the interrupt is

enabled and the stack is not full, the program will jump

to location 008H and begins execution.

· Location 00CH

This area is reserved for the 8-bit Timer Counter 1 in-

terrupt service program. If a timer interrupt results

from a Timer Counter 1 overflow, and if the interrupt is

enabled and the stack is not full, the program will jump

to location 00CH and begins execution.

Table Location

Any location in the ROM space can be used as look up

tables. The instructions

²TABRDC [m]² (used for any

bank) and

²TABRDL [m]² (only used for last page of pro-

gram ROM) transfer the contents of the lower-order byte

to the specified data memory [m], and the higher-order

byte to TBLH (08H). Only the destination of the

lower-order byte in the table is well-defined. The

higher-order bytes of the table word are transferred to

the TBLH. The table higher-order byte register (TBLH)

is read only.

The table pointer (TBLP) is a read/write register, which

indicates the table location.

Stack Register

- Stack

The stack register is a special part of the memory used

to save the contents of the Program Counter. This stack

is organized into four levels. It is neither part of the data

nor part of the program space, and cannot be read or

written to. Its activated level is indexed by a Stack

Pointer (SP) and cannot be read or written to. At a sub-

routine call or interrupt acknowledgment, the contents of

the program counter are pushed onto the stack.

The program counter is restored to its previous value

from the stack at the end of subroutine or interrupt rou-

tine, which is signaled by return instruction (RET or

RETI). After a chip resets, SP will point to the top of the

stack.

The interrupt request flag will be recorded but the ac-

knowledgment will be inhibited when the stack is full and

a non-masked interrupt takes place. After the stack

pointer is decremented (by RET or RETI), the interrupt

request will be serviced. This feature prevents stack

overflow and allows programmers to use the structure

more easily. In a similar case, if the stack is full and a

²CALL² is subsequently executed, stack overflow oc-

curs and the first entry is lost.

Instruction

Table Location

*10

TABRDC [m]

P10

TABRDL [m]

Table Location

Note: *10~*0: Current program ROM table

@7~@0: Write @7~@0 to TBLP pointer register

P10~P8: Bits of current program counter

0 0 0 0 H

0 0 0 4 H

0 0 0 8 H

P r o g r a m

R O M

0 0 0 C H

I n i t i a l A d d r e s s

T i m e B a s e I n t e r r u p t S u b r o u t i n e

T i m e r 0 I n t e r r u p t S u b r o u t i n e

T i m e r 1 I n t e r r u p t S u b r o u t i n e

0 7 F F H

0 0 1 5 H

Program Memory

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