Holtek BS82B12A-3, Руководство пользователя

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BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
BS82B12A-3/BS82C16A-3/BS82D20A-3
Touch Key 8-Bit Flash MCU with LED/LCD Driver
Special Vectors
Within the Program Memory, certain locations are reserved for the reset and interrupts. The location
0000H is reserved for use by the device reset for program initialisation. After a device reset is
initiated, the program will jump to this location and begin execution.
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 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 pair, the table data can be retrieved from the Program Memory
using the "TABRD[m]" or "TABRDL[m]" instructions respectively. When the instruction is
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
" 0 ".
The accompanying diagram illustrates the addressing data flow of the look-up table.
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
T B L P R e g i s t e r
D a t a
Ad
dr
es
s
1 6 b i t s
L a s t p a g e o r
T B H P R e g i s t e r
Table Program Example
The following example shows how the table pointer and table data is defined and retrieved from the
microcontroller. This example uses raw table data located in the Program Memory which is stored
there using the ORG statement. The value at this ORG statement is "0700H" which refers to the
start address of the last page within the
2 K words Program Memory of the BS82B12A-3. 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 "0706H" 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 specific
page if the "TABRD [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 "TABRD [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 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.