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HT82A836R Datasheet(PDF) 9 Page - Holtek Semiconductor Inc |
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HT82A836R Datasheet(HTML) 9 Page - Holtek Semiconductor Inc |
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9 / 75 page  HT82A836R Rev. 1.10 9 August 5, 2011 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 pointers must first be setup which point to the data in the Program Memory which is to be read. In this device there are two table pointers, the low byte pointer, TBLP and the high byte pointer, TBHP. However, the high byte pointer, TBHP, can only be used if it is enabled using configura- tion options. Using both table pointers enables any area in the Program Memory to be addressed while if only the low byte pointer, TBLP, is used then only the present page or last page can be addressed. If the configuration options do not enable the high byte pointer, then after setting up the low table pointer, TBLP, 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, respec- tively. When these instructions are executed, the lower order table byte from the Program Memory will be trans- ferred 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. The following diagram illustrates the addressing/data flow of the look-up table using the single table address pointer TBLP: If the configuration options enable the high table pointer, TBHP, then this register together with the low table pointer, TBLP, can be used together as a pair to point to any located in the Program Memory. 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 instructions are exe- cuted, 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. The following diagram illustrates the addressing/data flow of the look-up table using the dual table address pointers TBLP and TBHP: Table Program Example The following example shows how the table pointer and table data is defined and retrieved from the micro con- troller using the single table data pointer, TBLP. This ex- ample uses raw table data located in the last page which is stored there using the ORG statement. The value at this ORG statement is ²1F00H² which refers to the start address of the last page within the 8K Program Memory of device. The table pointer is setup here to have an ini- tial value of ²06H². This will ensure that the first data read from the data table will be at the Program Memory address ²1F06H² or 6locations after the start of the last page. Note that the value for the table pointer is refer- enced 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 the table read instructions. If using the table read instructions, the Interrupt Service Routines may change the value of TBLH and subsequently cause er- rors if used again by the main routine. As a rule it is rec- ommended 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 ] 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 Single Address Pointer Look-up Table P r o g r a m M e m o r y 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 T B H P H i g h b y t e o f t a b l e c o n t e n t s Dual Address Pointer Look-up Table |
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