HT95R55 datasheet(13/80 Pages) HOLTEK

13 / 80 page

HT95R54/HT95R55

Rev. 1.00

March 3, 2010

· Location 018H

This location is used by the Multi-function Interrupt. If

a falling edge transition is detected on PC0 or PC5, or

a rising edge transition is detected on PC7 or an

SPI/I2C interrupt occurs, or an external peripheral fall-

ing edge transition, or a timer 2 overflow, the program

will jump to this location and begin execution if the

multi-function interrupt is enabled and the stack is not

full.

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

²3F00H² which refers to

the start address of the last page within the 16K 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

²3F06H² 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.

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

b13

b12

b11

b10

TABRDC [m]

PC13 PC12 PC11 PC10

PC9

PC8

TABRDL [m]

111111

Table Location

Note:

For the HT95R54, the Table address location is 13 bits,i.e. from b12~b0.

For the HT95R55, the Table address location is 14 bits,i.e. from b13~b0.

PC13~PC8: Current Program Counter bits

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

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