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HT83F80 Datasheet(PDF) 10 Page - Holtek Semiconductor Inc |
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HT83F80 Datasheet(HTML) 10 Page - Holtek Semiconductor Inc |
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10 / 62 page  HT83FXX Rev. 1.30 10 June 7, 2010 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, table pointers are used to setup the address of the data that is to be accessed from the Program Memory. However, as some devices pos- sess only a low byte table pointer and other devices pos- sess both a high and low byte pointer it should be noted that depending upon which device is used, accessing look-up table data is implemented in slightly different ways. There are two Table Pointer Registers known as TBLP and TBHP in which the lower order and higher order ad- dress of the look-up data to be retrieved must be respec- tively first written. The additional TBHP register allows the complete address of the look-up table to be defined and consequently allow table data from any address and any page to be directly accessed. For this device, after setting up both the low and high byte table pointers, the table data can then be retrieved from any area of Program Memory using the ²TABRDC [m]² instruction or from the last page of the Program Memory using the ²TABRDL [m]² instruction. When either of these instruc- tions are 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 ²0². 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 devices. 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 ²700H² which refers to the start address of the last page within the 2048 ´15-bit 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 ²706H² 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 trans- ferred to the TBLH register automatically when the ²TABRDL [m]² instruction is executed. 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 P r o g r a m C o u n t e r H i g h B y t e Look-up Table 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 ²706H² 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 ²705H² 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 700h ; sets initial address of HT83F10/20/40/60/80 last page dc 00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh : : |
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