HT56R67 datasheet(18/104 Pages) HOLTEK

18 / 104 page

HT56R67/HT56R668/HT56C668/HT56R678/HT56C678/HT56R688

Rev. 1.20

March 4, 2010

Table Program Example

The following example shows how the table pointer and

table data is defined and retrieved from the HT56R678/

HT56C678. This example uses raw table data located in

the last page which is stored there using the ORG state-

ment. The value at this ORG statement is

²7F00H²

which refers to the start address of the last page within

the 32K Program Memory of the HT56R678/HT56C678

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

²7F06H² 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 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.

tempreg1 db

; temporary register #1

tempreg2 db

; 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

²7F06H² 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

²7F05H² transferred to

; tempreg2 and TBLH

; in this example the data

²1AH² is transferred to

; tempreg1 and data

²0FH² to register tempreg2

; the value

²00H² will be transferred to the high byte

; register TBLH

org 7F00h

; sets initial address of last page

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

HT56R67 Datasheet(PDF) 18 Page - Holtek Semiconductor Inc

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