HT86B05 datasheet(27/79 Pages) HOLTEK

27 / 79 page

HT86BXX/HT86BRXX

Rev. 1.60

October 20, 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.

For the devices, there are two Table Pointer Registers

known as TBLP and TBHP in which the lower order and

higher order address of the look-up data to be retrieved

must be respectively first written. Unlike the other de-

vices in which only the low address byte is defined using

the TBLP register, 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 these de-

vices, 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 in-

struction or from the last page of the Program Memory

using the

²TABRDL [m]² instruction. When either of

these instructions 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

byte will be read as

²0².

The following diagram illustrates the addressing/data

flow of the look-up table for the devices:

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

²1F00H² which re-

fers to the start address of the last page within the Pro-

gram Memory of the microcontroller. The table pointer is

setup here to have an initial value of

²06H². This will en-

sure that the first data read from the data table will be at

the Program Memory address

²1F06H² 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 transferred to the TBLH register

automatically when the

²TABRDL [m]² instruction is exe-

cuted.

P r o g r a m

M e m o r y

T B L P

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 H P

Look-up Table

tempreg1

; temporary register #1

tempreg2

; 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

²1F06H² 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

²1F05H² 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

1F00h

; sets initial address of HT86B60 last page

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

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