HT82B40A datasheet(9/54 Pages) HOLTEK

9 / 54 page

HT82B40R/HT82B40A

Rev. 1.70

November 5, 2014

in the TBLP and TBHP registers (if the configuration

option has disabled TBHP then the value in TBHP has

no effect). TBLH is read only and cannot be restored.

If the main routine and the ISR (Interrupt Service Rou-

tine) both employ the table read instruction, the con-

tents of the TBLH in the main routine are likely to be

changed by the table read instruction used in the ISR

and errors can occur. Using the table read instruction

in the main routine and the ISR simultaneously should

be avoided. However, if the table read instruction has

to be applied in both the main routine and the ISR, the

interrupt should be disabled prior to the table read in-

struction. It will not be enabled until the TBLH has

been backed up. All table related instructions require

two cycles to complete the operation. These areas

may function as normal program memory depending

on the requirements.

Once TBHP is enabled, the instruction

²TABRDC [m]²

reads the Program Memory data as defined by the

TBLP and TBHP values. If the Program Memory code

option has disabled TBHP, the instruction

²TABRDC

[m]

² reads the Program Memory data as defined by

TBLP only in the current Program Memory page.

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 TBLP register and the

higher order address in the TBHP register. These two

registers define the full address of the look-up table.

Using the TBHP must be selected by configuration op-

tion, if not used table data can still be accessed but only

the lower byte address in the current page or last page

can be defined.

After setting up the table pointers, 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.

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

²F00H² which refers to the start address of the last page

within the 4K Program Memory of device. The table

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

²F06H² 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.

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

Table Read

- TBLP only

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

T B H P

Table Read

- TBLP/TBHP

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