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HT56RB688 Datasheet(PDF) 26 Page - Holtek Semiconductor Inc |
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HT56RB688 Datasheet(HTML) 26 Page - Holtek Semiconductor Inc |
26 / 164 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 table pointer register, TBLP and TBHP. 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 specific Program Memory page or last Program Memory page using the ²TABRDC[m]² or ²TABRDL [m]² instructions, respectively. When these instructions 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 HT56RB688. This example uses raw table data located in the last page. The value at ²BF00H² which refers to the start address of the last page within the 48K Program Memory of the HT56RB688 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 ²BF06H² or 6 locations after the start of the last page. Note that the value for the table pointer is referenced to TBLP and TBHP registers 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 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. rombank 5 code5 ds .section ¢data¢ Tempreg1 db ? ; temporary register #1 tempreg2 db ? ; temporary register #2 : : code0 .section ¢code¢ mov a,06h ; initialise table pointer - note that this address ; is referenced mov tblp,a ; to the last page or the page that tbhp pointed Rev. 1.10 26 April 15, 2013 HT56RB688 TinyPowerTM A/D type Smart Card OTP MCU with LCD, DAC, ISO 7816 and USB Interfaces R e g i s t e r T B L H U s e r S e l e c t e d R e g i s t e r H i g h B y t e L o w B y t e L a s t p a g e o r T B H P R e g i s t e r T B L P R e g i s t e r D a t a 1 6 b i t s P r o g r a m M e m o r y |
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