HT86B40 datasheet(32/83 Pages) HOLTEK

32 / 83 page

HT86BXX/HT86BRXX

Rev. 1.70

February 22, 2010

data .section

¢data¢

adres1

db ?

adres2

db ?

adres3

db ?

adres4

db ?

block

db ?

code .section at 0

¢code¢

org

00h

start:

mov a,04h

; setup size of block

mov block,a

mov a,offset adres1

; Accumulator loaded with first RAM address

mov mp0,a

; setup memory pointer with first RAM address

loop:

clr IAR0

; clear the data at address defined by MP0

inc mp0

; increment memory pointer

sdz block

; check if last memory location has been cleared

jmp loop

continue:

The important point to note here is that in the example shown above, no reference is made to specific RAM addresses.

Bank Pointer

- BP

The RAM Data Memory is divided into two Banks,

known as Bank 0 and Bank 1. With the exception of the

BP register, all of the Special Purpose Registers and

General Purpose Registers are contained in Bank 0. If

data in Bank 0 is to be accessed, then the BP register

must be loaded with the value "00", while if data in Bank

1 is to be accessed, then the BP register must be loaded

with the value

²01².

Using Memory Pointer MP0 and Indirect Addressing

spective of the value of the Bank Pointer.

The Data Memory is initialised to Bank 0 after a reset,

except for the WDT time-out reset in the Power Down

Mode, in which case, the Data Memory bank remains

unaffected. It should be noted that Special Function

Data Memory is not affected by the bank selection,

which means that the Special Function Registers can be

accessed from within either Bank 0 or Bank 1. Directly

addressing the Data Memory will always result in Bank 0

being accessed irrespective of the value of the Bank

Pointer.

Accumulator

- ACC

The Accumulator is central to the operation of any

microcontroller and is closely related with operations

carried out by the ALU. The Accumulator is the place

where all intermediate results from the ALU are stored.

Without the Accumulator it would be necessary to write

the result of each calculation or logical operation such

as addition, subtraction, shift, etc., to the Data Memory

resulting in higher programming and timing overheads.

Data transfer operations usually involve the temporary

storage function of the Accumulator; for example, when

transferring data between one user defined register and

another, it is necessary to do this by passing the data

through the Accumulator as no direct transfer between

two registers is permitted.

Program Counter Low Register

- PCL

To provide additional program control functions, the low

byte of the Program Counter is made accessible to pro-

grammers by locating it within the Special Purpose area

of the Data Memory. By manipulating this register, direct

jumps to other program locations are easily imple-

mented. Loading a value directly into this PCL register

will cause a jump to the specified Program Memory lo-

cation, however, as the register is only 8-bit wide, only

jumps within the current Program Memory page are per-

mitted. When such operations are used, note that a

dummy cycle will be inserted.

Look-up Table Registers

- TBLP, TBLH

These two special function registers are used to control

operation of the look-up table which is stored in the Pro-

gram Memory. TBLP is the table pointer and indicates

the location where the table data is located. Its value

must be setup before any table read commands are ex-

ecuted. Its value can be changed, for example using the

²INC² or ²DEC² instructions, allowing for easy table data

pointing and reading. TBLH is the location where the

B a n k P o i n t e r

b 7

b 0

B P 0

D a t a M e m o r y

B a n k 0

B a n k 1

N o t u s e d , m u s t b e r e s e t t o " 0 "

Bank Pointer

- BP

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