BS86B12A-3 Datasheet, PDF (32/195 Pages) Holtek Semiconductor Inc – Touch A/D Flash MCU with LED/LCD Driver

BS86B12A-3/BS86C16A-3/BS86D20A-3
Touch A/D Flash MCU with LED/LCD Driver
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 memory [m] is located
in Data Memory Sector 0. If the memory [m] is located in Data Memory other sectors, the data can
be retrieved from the program memory using the “LTABRD[m]” or “LTABRDL[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.
The accompanying diagram illustrates the addressing data flow of the look-up table.
Lastpage or
T B H P R e g is te r
T B L P R e g is te r
P ro g ra m M e m o ry
D a ta
1 6 b its
R e g is te r T B L H
H ig h B y te
U s e r S e le c te d
R e g is te r
L o w B y te
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 “0F00H” which refers to the
start address of the last page within the 4K words Program Memory of the BS86C16A-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 “0F06H” 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/write register and can 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.
Rev. 1.40
32
December 05, 2016