HT56R656 datasheet(20/108 Pages) HOLTEK

20 / 108 page

HT56R62/HT56R65

HT56R642/HT56R644/HT56R654/HT56R656

Rev. 1.00

July 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, the table pointer must

first be setup by placing the lower order address of the

look up data to be retrieved in the table pointer register,

TBLP. This register defines the lower 8-bit address of

the look-up table.

After setting up the table pointer, the table data can be

retrieved from the current Program Memory page or last

Program Memory page using the

²TABRDC[m]² or

²TABRDL [m]² instructions, respectively. When these in-

structions are executed, the lower order table byte from

the Program Memory will be transferred to the user de-

fined Data Memory register [m] as specified in the in-

struction. 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:

Table Program Example

The following example shows how the table pointer and

table data is defined and retrieved from the

microcontroller. This example uses raw table data lo-

cated 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 2K Program Memory of the HT56R62. The ta-

ble pointer is setup here to have an initial value of

²06H².

This will ensure that the first data read from the data ta-

ble 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 ad-

dress of the present page if the

²TABRDC [m]² instruc-

tion 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 in-

struction is executed.

Because the TBLH register is a read-only register and

cannot be restored, care should be taken to ensure its

protection if both the main routine and Interrupt Service

Routine use table read instructions. If using the table

read instructions, the Interrupt Service Routines may

change the value of the TBLH and subsequently cause

errors if used again by the main routine. As a rule it is

recommended that simultaneous use of the table read

instructions should be avoided. However, in situations

where simultaneous use cannot be avoided, the inter-

rupts should be disabled prior to the execution of any

main routine table-read instructions. Note that all table

related instructions require two instruction cycles to

complete their operation.

P r o g r a m

M e m o r y

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

H i g h B y t e

T B L P

T B L H

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

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

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

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

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

org 700h

; sets initial address of last page

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

HT56R656 数据表(PDF) 20 Page - Holtek Semiconductor Inc

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