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On the 17Cxxx and 18Cxxx PICs, you can access program memory via the 'table
read' instructions.
On the 16Fxxx PICs, you can access program memory via a set of SFR
(special function registers).
On all other PICs, you'll have to use a 'computed GOTO/RETW-style' table.
dt - Data Table.
Generates a series of RETLW instructions, one instruction for each expr. Each expr must be an 8-bit value. Each character in a string is stored in its own RETLW instruction.
Simple Example
dt "A Message", 0
dt FirstValue, SecondValue, EndOfValues
T
; Get the prime number indicated by W. The first prime number is 2 and is
; indicated by W being 0. W = 1 results in 3, W = 2 in 5, etc. The
; prime number will be in W.
;
; WARNING: This code has not been tested, not even syntax checked.
;
movwf tblptrl ;save table offset
movlw upper prime
movwf tblptru ;init table entry address high byte
movlw high prime
movwf tblptrh ;init table entry address middle byte
movlw low prime
addwf tblptrl ;make table entry address low byte
movlw 0
addwfc tblptrh ;propagate carry to make final entry address
addwfc tblptru
tblrd* ;read the addressed byte into TABLAT
movf tablat, w ;get the indexed table value into W
...
.prime code_pack
prime ;table of prime numbers
db 2 ;table index 0
db 3 ;table index 1
db 5
db 7
db 11
db 13
db 17
...
TABLE1:
movwf POINTER ;save table offset
clrf PCLATU
movlw HIGH (DATAS)
movwf PCLATH
rlncf POINTER,W
addlw LOW (DATAS)
btfsc STATUS,C
incf PCLATH,F
movwf PCL
DATAS:
retlw ' '
retlw 'O '
retlw 'P'
retlw 'E'
retlw 'N'
retlw ':'
;mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
In 18F series, use tablat*+
TABLE1:
; Set up table pointers and send a messag to LCD
movlw UPPER(MSG)
movwf TBLPTRU
movlw HIGH(MSG)
movwf TBLPTRH
movlw LOW(MSG)
movwf TBLPTRL
tblrd *+ ; Read the table character to tablat, then increment tblptr
movf TABLAT,W ; Get the character from the table (MSG)
return
MSG:
DB "INICIALIZANDO!!!",0x00
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