BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 17

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

BS2824/BS2854/BS2868
Touch Key MCU
The following diagram illustrates the addressing/data flow of the look-up table:
Table Program Example
The accompanying 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 700H which refers to the start address of the
last page within the 2K Program Memory of the BS2854 device. The table pointer is setup here to
have an initial value of 06H . This will ensure that the first data read from the data table will be at
the Program Memory address 706H 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 TABRDC [m]
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 TABRDL [m] 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 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.
Rev. 1.00
17
January 27, 2010