Rev. 1.10
16
November 26, 2019
Rev. 1.10
17
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
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
Ad
dr
es
s
1 6 b i t s
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 "F00H" which refers to the start
address of the last page within the 4K Program Memory of the microcontroller. 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 "F06H" 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
"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.
Table Read Program Example
tempreg1 db ? ; temporary register #1
tempreg2 db ? ; temporary register #2
:
mov a, 06h ; initialise low table pointer - note that this address
mov
tblp,
a
;
is
referenced
mov
a,
0Fh
;
initialise
high
table
pointer
mov tbhp, a
:
tabrd tempreg1 ; transfers value in table referenced by table pointer data at
program
;
memory
address
F06H
transferred
to
tempreg1
and
TBLH
dec tblp ; reduce value of table pointer by one
tabrd tempreg2 ; transfers value in table referenced by table pointer data at
program
; memory address F05H transferred to tempreg2 and TBLH in this
; example the data 1AH is transferred to tempreg1 and data 0FH to
;
register
tempreg2
:
org
F00h
;
sets
initial
address
of
program
memory
dc 00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh
:
:
