HT46R4A
cated in the last page which is stored there using the
ORG statement. The value at this ORG statement is
²F00H² which refers to the start address of the last page
within the 4K Program Memory. The table pointer is
setup here to have an initial value of ²06H². This will en-
sure that the first data read from the data table will be at
the Program Memory address ²F06H² or 6 locations af-
ter 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 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 ex-
ecuted.
The diagram illustrates the addressing/data flow of the
look-up table:
P
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[
m
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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 lo-
tempreg1
tempreg2
db
db
:
?
?
; temporary register #1
; temporary register #2
:
mov
mov
a,06h
; initialise table pointer - note that this address
; is referenced
tblp,a
:
:
; to the last page or present page
tabrdl
tempreg1
; transfers value in table referenced by table pointer
; to tempregl
; data at prog. memory address ²F06H² transferred to
; tempreg1 and TBLH
dec
tblp
; reduce value of table pointer by one
tabrdl
tempreg2
; transfers value in table referenced by table pointer
; to tempreg2
; data at prog.memory address ²F05H² transferred to
; tempreg2 and TBLH
; in this example the data ²1AH² is transferred to
; tempreg1 and data ²0FH² to register tempreg2
; the value ²00H² will be transferred to the high byte
; register TBLH
:
:
org
dc
F00h
; sets initial address of last page
00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh
:
:
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 Location Bits
Instruction
b11
TABRDC[m] PC11 PC10 PC9
TABRDL [m]
b10
b9
b8
PC8
1
b7
@7
@7
b6
@6
@6
b5
@5
@5
b4
@4
@4
b3
@3
@3
b2
@2
@2
b1
@1
@1
b0
@0
@0
1
1
1
Table Location
Note: PC11~PC8: Current Program Counter bits
@7~@0: Table Pointer TBLP bits
The Table address location is 12 bits, i.e. from b11~b0.
Rev. 1.00
9
November 28, 2007
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
