HT82M9BA datasheet(7/44 Pages) HOLTEK

7 / 44 page

HT82M9BE/HT82M9BA

Rev. 1.80

December 22, 2008

data as defined by TBLP and the current program

counter bits.

Stack Register

- STACK

This is a special part of the memory which is used to

save the contents of the program counter only. The

stack is organized into 8 levels and is neither part of the

data nor part of the program space, and is neither read-

able nor writeable. The activated level is indexed by the

stack pointer (SP) and is neither readable nor writeable.

At a subroutine call or interrupt acknowledge signal, the

contents of the program counter are pushed onto the

stack. At the end of a subroutine or an interrupt routine,

signaled by a return instruction (RET or RETI), the pro-

gram counter is restored to its previous value from the

stack. After a chip reset, the SP will point to the top of the

stack.

If the stack is full and a non-masked interrupt takes

place, the interrupt request flag will be recorded but the

acknowledge signal will be inhibited. When the stack

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

will be serviced. This feature prevents stack overflow al-

lowing the programmer to use the structure more easily.

In a similar case, if the stack is full and a

²CALL² is sub-

sequently executed, stack overflow occurs and the first

entry will be lost (only the most recent 4 return ad-

dresses are stored).

Data Memory

- RAM for Bank 0

The data memory is designed with 224

´8 bits. The data

memory is divided into two functional groups: special

function registers and general purpose data memory

(224

´8). Most are read/write, but some are read only.

The unused spaces before the 20H is reserved for fu-

ture expanded usage and reading these locations will

get

²00H². The general purpose data memory, ad-

dressed from 20H to FFH, is used for data and control

information under instruction commands.

All of the data memory areas can handle arithmetic,

logic, increment, decrement and rotate operations di-

rectly. Except for some dedicated bits, each bit in the

data memory can be set and reset by

²SET [m].i² and

²CLR [m].i². They are also indirectly accessible through

memory pointer registers (MP0 or MP1).

Data Memory

- RAM for Bank 1

The special function registers used in the USB interface

are located in RAM Bank1. In order to access Bank1

be used and the Bank register BP should be set to 1.

The RAM bank 1 mapping is as shown.

Address 00~1FH in RAM Bank0 and Bank1 are located

in the same Registers

Indirect Addressing Register

Locations 00H and 02H are indirect addressing regis-

ters that are not physically implemented. Any read/write

operation on [00H] ([02H]) will access the data memory

pointed to by MP0 (MP1). Reading location 00H (02H)

indirectly will return the result 00H. Writing indirectly re-

sults in no operation.

The indirect addressing pointer (MP0) always points to

Bank0 RAM addresses no matter the value of Bank

The indirect addressing pointer (MP1) can access

Bank0 or Bank1 RAM data according to the value of BP

which is set to

²0² or ²1² respectively.

The memory pointer registers (MP0 and MP1) are 8-bit

registers.

0 0 H

0 1 H

0 2 H

0 3 H

0 4 H

0 5 H

0 6 H

0 7 H

0 8 H

0 9 H

0 A H

0 B H

0 C H

0 D H

0 E H

0 F H

1 0 H

1 1 H

1 2 H

1 3 H

1 4 H

1 5 H

1 6 H

1 7 H

1 8 H

G e n e r a l P u r p o s e

D a t a M e m o r y

( 2 2 4 B y t e s )

1 A H

1 B H

1 C H

1 D H

1 E H

1 F H

F F H

2 0 H

I n d i r e c t A d d r e s s i n g R e g i s t e r 0

M P 0

I n d i r e c t A d d r e s s i n g R e g i s t e r 1

M P 1

B P

A C C

P C L

T B L P

T B L H

W D T S

S T A T U S

I N T C

T M R 0

T M R 0 C

T M R 1 H

T M R 1 L

T M R 1 C

P A

P A C

P B

P B C

P C

P C C

U S C

U S R

S C C

T B H P

B a n k 0

1 9 H

Bank 0 RAM Mapping

HT82M9BA Datasheet(PDF) 7 Page - Holtek Semiconductor Inc

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