HT95R23 datasheet(9/53 Pages) HOLTEK

9 / 53 page

HT95R23

Rev. 1.00

March 25, 2008

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, .

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 have uncertain values.

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 device. 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

²F00H² which refers to

the start address of the last page within the 4K 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

²F06H² 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 automati-

cally when the

²TABRDL [m]² instruction 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 ]

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

Look-up Table

Instruction

Table Location Bits

b11

b10

TABRDC [m]

PC11

PC10

PC9

PC8

@7@6@5@4@3@2@1@0

TABRDL [m]

1111

Table Location

Note:

PC11~PC8: Current Program Counter bits

@7~@0: Table Pointer Lower-order bits (TBLP)

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