HT45R37
Table Program Example
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 inter-
rupts 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.
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-
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 of the HT45R37. The ta-
ble pointer is setup here to have an initial value of ²06H².
This will ensure that the first data read from the data ta-
ble will be at the Program Memory address ²F06H² or 6
locations after the start of the last page. Note that the
value for the table pointer is referenced to the first ad-
dress of the present page if the ²TABRDC [m]² instruc-
tion 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 in-
struction is executed.
Tempreg1
tempreg2
db
db
?
?
; temporary register #1
; temporary register #2
:
:
mov
a,06h
; initialise table pointer - note that this address
; is referenced
mov
:
tblp,a
; to the last page or present page
:
tabrdl
tempreg1
tempreg2
; transfers value in table referenced by table pointer
; to tempregl
; data at prog. memory address ²F06H² transferred to
; tempreg1 and TBLH
dec tblp
tabrdl
; reduce value of table pointer by one
; 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
:
:
org F00h
; sets initial address of last page
dc 00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh
:
:
Rev. 1.20
13
February 25, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
