HT83F40P datasheet(10/61 Pages) HOLTEK

10 / 61 page

HT83FXX

Rev. 1.00

May 12, 2009

Look-up Table

Any location within the Program Memory can be defined

as a look-up table where programmers can store fixed

data. To use the look-up table, table pointers are used to

setup the address of the data that is to be accessed from

the Program Memory. However, as some devices pos-

sess only a low byte table pointer and other devices pos-

sess both a high and low byte pointer it should be noted

that depending upon which device is used, accessing

look-up table data is implemented in slightly different

ways.

There are two Table Pointer Registers known as TBLP

and TBHP in which the lower order and higher order ad-

dress of the look-up data to be retrieved must be respec-

tively first written. The additional TBHP register allows

the complete address of the look-up table to be defined

and consequently allow table data from any address

and any page to be directly accessed. For this device,

after setting up both the low and high byte table pointers,

the table data can then be retrieved from any area of

Program Memory using the

²TABRDC [m]² instruction or

from the last page of the Program Memory using the

²TABRDL [m]² instruction. When either of these instruc-

tions are executed, the lower order table byte from the

Program Memory will be transferred to the user defined

Data Memory register [m] as specified in the instruction.

The higher order table data byte from the Program

Memory will be transferred to the TBLH special register.

Any unused bits in this transferred higher order byte will

be read as

²0².

The following diagram illustrates the addressing/data

flow of the look-up table.

Table Program Example

The following example shows how the table pointer and

table data is defined and retrieved from the devices.

This example uses raw table data located in the last

page which is stored there using the ORG statement.

The value at this ORG statement is

²700H² which refers

to the start address of the last page within the

2048

´15-bit Program Memory of the microcontroller.

The table pointer is setup here to have an initial value of

²06H². This will ensure that the first data read from the

data table will be at the Program Memory address

²706H² or 6 locations after the start of the last page.

Note that the value for the table pointer is referenced to

the first address of the present page if the

²TABRDC

[m]

² instruction is being used. The high byte of the table

data which in this case is equal to zero will be trans-

ferred to the TBLH register automatically when the

²TABRDL [m]² instruction is executed.

P r o g r a m

M e m o r y

T B L H

S p e c i f i e d b y [ m ]

H i g h B y t e o f T a b l e C o n t e n t s

L o w B y t e o f T a b l e C o n t e n t s

T B L P

P r o g r a m C o u n t e r

H i g h B y t e

Look-up Table

tempreg1 db

; temporary register #1

tempreg2 db

; temporary register #2

mov a,06h

; initialise table pointer - note that this address is referenced

mov tblp,a

; to the last page or present page

tabrdl

tempreg1

; transfers value in table referenced by table pointer

; to tempregl

; data at prog. memory address

²706H² transferred to

; tempreg1 and TBLH

dec tblp

; reduce value of table pointer by one

tabrdl

tempreg2

; transfers value in table referenced by table pointer

; to tempreg2

; data at prog.memory address

²705H² transferred to

; tempreg2 and TBLH

; in this example the data

²1AH² is transferred to

; tempreg1 and data

²0FH² to register tempreg2

; the value

²00H² will be transferred to the high byte

; register TBLH

org 700h

; sets initial address of HT83F10/20/40/60/80 last page

00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh

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