SN8P2711A
8-Bit Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 18
Version 0.1
2.1.1.3
LOOK-UP TABLE DESCRIPTION
In the ROM’s data lookup function, Y register is pointed to middle byte address (bit 8~bit 15) and Z register is pointed
to low byte address (bit 0~bit 7) of ROM. After MOVC instruction executed, the low-byte data will be stored in ACC and
high-byte data stored in R register.
¾
Example: To look up the ROM data located “TABLE1”.
B0MOV
Y, #TABLE1$M
; To set lookup table1’s middle address
B0MOV
Z, #TABLE1$L
; To set lookup table1’s low address.
MOVC
; To lookup data, R = 00H, ACC = 35H
; Increment the index address for next address.
INCMS Z
;
Z+1
JMP
@F
; Z is not overflow.
INCMS
Y
; Z overflow (FFH
Æ
00),
Æ
Y=Y+1
NOP
;
;
@@:
MOVC
; To lookup data, R = 51H, ACC = 05H.
…
;
TABLE1:
DW
0035H
; To define a word (16 bits) data.
DW
5105H
DW
2012H
…
Note:
The Y register will not increase automatically when Z register crosses boundary from 0xFF to
0x00. Therefore, user must take care
such
situation to avoid
look-up table errors.
If
Z
register
overflows, Y register must be added one. The following INC_YZ macro shows a simple method
to process Y and Z registers automatically.
¾
Example: INC_YZ macro.
INC_YZ
MACRO
INCMS
Z
; Z+1
JMP
@F
; Not overflow
INCMS
Y
; Y+1
NOP
; Not overflow
@@:
ENDM
