HT46R0664 datasheet(17/92 Pages) HOLTEK

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Rev. 1.00

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Rev. 1.00

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HT46R0664

Enhanced A/D+LCD 8-Bit OTP MCU

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 address

of the look up data to be retrieved in the table pointer register, TBLP. These registers define the

total address of the look-up table. After setting up the table pointer, the table data can be retrieved

from the Program Memory using the “TABRD [m]” instructions, respectively. When the instruction

is 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 “0”. The accompanying diagram illustrates the

addressing data flow of the look-up table.

PC High Byte

Last page or

present page

PC11~PC8

Data

16 bits

Program Memory

High Byte

Low Byte

User Selected

TBLP Register

Instruction

Table Location Bits

b11

b10

T�BRDC [m]

PC11 PC10 PC9 PC8 @7

@�

T�BRDL [m]

@�

PC11~PC8: Current Program Counter bits

@7~@0: Table Pointer TBLP bits

b11~b0: Table address location bits

Table Program Example

The accompanying 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 “F00H” 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 “06H”. This will ensure that the first data

read from the data table will be at the Program Memory address “F06H” 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 “TABRDC [m]” 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 “TABRDL [m]” 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 the table read instructions. If using the table read instructions, the

Interrupt Service Routines may change the value of 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 interrupts 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.

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