Holtek HT46R22, Handbook

Page: 30 / 162

The following diagram illustrates the addressing/data flow of the look-up table:
Table Program Example
The following example shows how the table pointer and table data is defined and retrieved from
the HT46R47 A/D microcontroller. This example uses raw table data located in the last page which
is stored there using the ORG statement. The value at this ORG statement is
²
700
²
hex which re-
fers to the start address of the last page within the 2K Program Memory of the HT46R47
microcontroller. The table pointer is setup here to have an initial value of 06 hex.
This will ensure that the first data read from the data table will be at the Program Memory address
706 hex or 6 locations after the start of the last page. Note that the value for the table pointer is ref-
erenced to the first address of the present page if the
²
TABRDC [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 regis-
ter automatically when the
²
TABRDL [m]
²
instruction is executed.
tempreg1 db ? ; temporary register #1
tempreg2 db ? ; temporary register #2
:
:
mov a,06h ; initialize table pointer - note that this address
; is referenced
mov 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 706H 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 705H transferred to
; tempreg2 and TBLH
; in this example the data
²
1A
²
is transferred to
; tempreg1 and data
²
0F
²
to register tempreg2
; the value
²
0
²
will be transferred to the high byte
; register TBLH
:
:
org 700h ; sets initial address of last page (for HT46R47)
dc 00Ah, 00Bh, 00Ch, 00Dh, 00Eh, 00Fh, 01Ah, 01Bh
:
:
Chapter 1 Hardware Structure
21
P r o g r a m
M e m o r y
P r o g r a m C o u n t e r
h i g h b y t e
T B L P
T B L H S p e c i f i e d b y [ m ]
H i g h b y t e o f t a b l e c o n t e n t s
L o w b y t e o f t a b l e c o n t e n t s